Statement Of Cash Flows [Abstract]
| Concept |
2021-01-01 to 2021-12-31 |
2021-01-01 to 2021-12-31 |
2021-01-01 to 2021-12-31 |
2021-01-01 to 2021-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
2019-01-01 to 2019-12-31 |
2019-01-01 to 2019-12-31 |
2019-01-01 to 2019-12-31 |
2019-01-01 to 2019-12-31 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Statement of cash flows [abstract] | ||||||||||||
| Cash flows from (used in) operating activities [abstract] | ||||||||||||
| Profit (loss) |
19,000,000
GBP
|
1,365,000,000
GBP
|
1,384,000,000
GBP
|
1,365,000,000
GBP
|
452,000,000
GBP
|
471,000,000
GBP
|
19,000,000
GBP
|
452,000,000
GBP
|
714,000,000
GBP
|
714,000,000
GBP
|
733,000,000
GBP
|
19,000,000
GBP
|
| Adjustments to reconcile profit (loss) [abstract] | ||||||||||||
| Adjustments for income tax expense | — | — |
504,000,000
GBP
|
— | — |
134,000,000
GBP
|
— | — | — | — |
279,000,000
GBP
|
— |
| Adjustments for depreciation and amortisation expense | — | — |
501,000,000
GBP
|
— | — |
562,000,000
GBP
|
— | — | — | — |
543,000,000
GBP
|
— |
| Adjustments for impairment loss (reversal of impairment loss) recognised in profit or loss | — | — |
228,000,000
GBP
|
— | — |
672,000,000
GBP
|
— | — | — | — |
239,000,000
GBP
|
— |
| Adjustments for provisions | — | — |
381,000,000
GBP
|
— | — |
273,000,000
GBP
|
— | — | — | — |
441,000,000
GBP
|
— |
| Adjustments for unrealised foreign exchange losses (gains) | — | — |
542,000,000
GBP
|
— | — |
410,000,000
GBP
|
— | — | — | — |
1,079,000,000
GBP
|
— |
| Other adjustments for non-cash items | — | — |
147,000,000
GBP
|
— | — |
267,000,000
GBP
|
— | — | — | — |
439,000,000
GBP
|
— |
| Adjustments to reconcile profit (loss) | — | — |
1,049,000,000
GBP
|
— | — |
1,412,000,000
GBP
|
— | — | — | — |
1,098,000,000
GBP
|
— |
| Income taxes paid (refund), classified as operating activities | — | — |
427,000,000
GBP
|
— | — |
159,000,000
GBP
|
— | — | — | — |
292,000,000
GBP
|
— |
| Cash flows from (used in) operating activities | — | — |
10,846,000,000
GBP
|
— | — |
18,823,000,000
GBP
|
— | — | — | — |
4,030,000,000
GBP
|
— |
| Cash flows from (used in) investing activities [abstract] | ||||||||||||
| Cash flows from (used in) investing activities | — | — |
3,077,000,000
GBP
|
— | — |
6,636,000,000
GBP
|
— | — | — | — |
2,890,000,000
GBP
|
— |
| Cash flows from (used in) financing activities [abstract] | ||||||||||||
| Proceeds from issuing other equity instruments | — | — |
210,000,000
GBP
|
— | — |
—
GBP
|
— | — | — | — |
500,000,000
GBP
|
— |
| Payments of lease liabilities, classified as financing activities | — | — |
25,000,000
GBP
|
— | — |
45,000,000
GBP
|
— | — | — | — |
54,000,000
GBP
|
— |
| Dividends paid, classified as financing activities | — | — |
1,358,000,000
GBP
|
— | — |
129,000,000
GBP
|
— | — | — | — |
315,000,000
GBP
|
— |
| Cash flows from (used in) financing activities | — | — |
10,753,000,000
GBP
|
— | — |
6,773,000,000
GBP
|
— | — | — | — |
4,180,000,000
GBP
|
— |
| Increase (decrease) in cash and cash equivalents before effect of exchange rate changes | — | — |
3,170,000,000
GBP
|
— | — |
18,686,000,000
GBP
|
— | — | — | — |
2,740,000,000
GBP
|
— |
| Effect of exchange rate changes on cash and cash equivalents [abstract] | ||||||||||||
| Effect of exchange rate changes on cash and cash equivalents | — | — |
18,000,000
GBP
|
— | — |
45,000,000
GBP
|
— | — | — | — |
53,000,000
GBP
|
— |