Profit Or Loss [Abstract]
| Concept | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Profit or loss [abstract] | ||||||||||||||||||||
| Profit (loss) [abstract] | ||||||||||||||||||||
| Revenue | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Insurance revenue | — | — | — | — | — | — | 
                                                9,601,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | 
                                                8,095,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Other income | — | — | — | — | — | — | 
                                                107,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | 
                                                372,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Other expense, by function | — | — | — | — | — | — | 
                                                821,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | 
                                                927,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Insurance service expenses from insurance contracts issued | — | — | — | — | — | — | 
                                                8,739,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | 
                                                7,628,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Income (expenses) from reinsurance contracts held, other than finance income (expenses) | — | — | — | — | — | — | 
                                                90,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | 
                                                27,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Share of profit (loss) of associates and joint ventures accounted for using equity method | — | — | — | — | — | — | 
                                                28,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | 
                                                11,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Profit (loss) before tax | — | — | — | — | — | — | 
                                                1,608,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | 
                                                1,389,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Tax expense (income) | — | — | — | — | — | — | 
                                                383,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | 
                                                275,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Profit (loss) from continuing operations | — | — | — | — | — | — | 
                                                1,065,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | 
                                                1,003,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Profit (loss) from discontinued operations | — | — | — | — | — | — | 
                                                121,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | 
                                                82,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Profit (loss) | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                946,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                946,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                2,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                944,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                1,086,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                1,086,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                1,086,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
| Profit (loss), attributable to [abstract] | ||||||||||||||||||||
| Profit (loss), attributable to owners of parent | — | — | — | — | — | — | 
                                                882,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | 
                                                1,038,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Profit (loss), attributable to non-controlling interests | — | — | — | — | — | — | 
                                                2,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | 
                                                0
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Earnings per share [text block] | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Earnings per share [abstract] | ||||||||||||||||||||
| Earnings per share [line items] | ||||||||||||||||||||
| Basic earnings per share [abstract] | ||||||||||||||||||||
| Basic earnings (loss) per share from continuing operations | — | — | — | — | — | — | 
                                                4.76
                                                
                                             | — | — | — | 
                                                5.34
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Basic earnings (loss) per share from discontinued operations | — | — | — | — | — | — | 
                                                0.57
                                                
                                             | — | — | — | 
                                                0.46
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Basic earnings (loss) per share | — | — | — | — | — | — | 
                                                4.19
                                                
                                             | — | — | — | 
                                                5.80
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Diluted earnings per share [abstract] | ||||||||||||||||||||
| Diluted earnings (loss) per share from continuing operations | — | — | — | — | — | — | 
                                                4.39
                                                
                                             | — | — | — | 
                                                4.85
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Diluted earnings (loss) per share from discontinued operations | — | — | — | — | — | — | 
                                                0.52
                                                
                                             | — | — | — | 
                                                0.41
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Diluted earnings (loss) per share | — | — | — | — | — | — | 
                                                3.87
                                                
                                             | — | — | — | 
                                                5.26
                                                
                                             | — | — | — | — | — | — | — | — | — |