Subclassifications Of Assets, Liabilities And Equities [Abstract]
| Concept | As at 2021-12-31 | As at 2020-12-31 | As at 2019-12-31 | 
|---|---|---|---|
| Subclassifications of assets, liabilities and equities [abstract] | |||
| Intangible assets and goodwill [abstract] | |||
| Goodwill | 
                                                5,630,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                5,630,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Investment property [abstract] | |||
| Investment property | 
                                                10,759,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                11,310,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Categories of financial assets [abstract] | |||
| Financial assets at fair value through profit or loss [abstract] | |||
| Financial assets at fair value through profit or loss | 
                                                293,983,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                267,652,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Financial assets at fair value through other comprehensive income [abstract] | |||
| Financial assets at fair value through other comprehensive income | 
                                                859,106,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                716,006,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Financial assets at amortised cost | 
                                                687,185,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                463,289,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Cash and cash equivalents [abstract] | |||
| Cash [abstract] | |||
| Balances with banks | 
                                                182,425,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                188,068,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Cash and cash equivalents | 
                                                2,142,718,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                2,097,672,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                2,023,273,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
| Miscellaneous assets [abstract] | |||
| Loans and advances | — | — | — | 
| Loans and advances to customers | 
                                                3,120,638,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                2,784,460,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Cash and bank balances at central banks | 
                                                1,963,552,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                1,912,743,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Reverse repurchase agreements and cash collateral on securities borrowed | 
                                                356,982,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                359,672,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Other assets | 
                                                52,327,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                49,404,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Borrowings, by type [abstract] | |||
| Bonds issued | 
                                                25,450,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                25,451,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Miscellaneous liabilities [abstract] | |||
| Deposit liabilities | — | — | — | 
| Deposits from banks | 
                                                52,893,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                66,052,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Deposits from customers [abstract] | |||
| Deposits from customers | 
                                                6,946,583,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                6,190,947,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Other liabilities | 
                                                67,722,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                61,160,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Issued capital [abstract] | |||
| Issued capital | 
                                                127,130,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                127,130,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Accumulated other comprehensive income [abstract] | |||
| Reserve of exchange differences on translation | 
                                                89,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                133,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Net assets (liabilities) [abstract] | |||
| Assets | 
                                                7,701,310,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                6,930,418,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Liabilities | 
                                                7,093,361,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | 
                                                6,344,613,000
                                                
                                                    
                                                        BGN
                                                    
                                                
                                             | — | 
| Assets less current liabilities [abstract] |