Statement Of Changes In Equity [Abstract]
| Concept |
As at 2021-12-31 |
As at 2021-12-31 |
2021-01-01 to 2021-12-31 |
As at 2021-12-31 |
2021-01-01 to 2021-12-31 |
2021-01-01 to 2021-12-31 |
2021-01-01 to 2021-12-31 |
As at 2021-12-31 |
2021-01-01 to 2021-12-31 |
As at 2021-12-31 |
As at 2021-12-31 |
As at 2021-12-31 |
2021-01-01 to 2021-12-31 |
2021-01-01 to 2021-12-31 |
2020-01-01 to 2020-12-31 |
As at 2020-12-31 |
As at 2020-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
As at 2020-12-31 |
As at 2020-12-31 |
As at 2020-12-31 |
As at 2020-12-31 |
As at 2020-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
As at 2019-12-31 |
As at 2019-12-31 |
As at 2019-12-31 |
As at 2019-12-31 |
As at 2019-12-31 |
As at 2019-12-31 |
As at 2019-12-31 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Statement of changes in equity [abstract] | |||||||||||||||||||||||||||||||||||
| Statement of changes in equity [line items] | |||||||||||||||||||||||||||||||||||
| Equity |
1,386,700,000
GBP
|
1,073,700,000
GBP
|
— |
11,600,000
GBP
|
— | — | — |
1,013,000,000
GBP
|
— |
1,288,500,000
GBP
|
9,300,000
GBP
|
161,200,000
GBP
|
— | — | — |
1,135,700,000
GBP
|
7,100,000
GBP
|
— | — | — |
1,153,500,000
GBP
|
3,100,000
GBP
|
—
GBP
|
153,300,000
GBP
|
175,100,000
GBP
|
— | — | — |
6,400,000
GBP
|
—
GBP
|
30,400,000
GBP
|
778,600,000
GBP
|
909,300,000
GBP
|
100,800,000
GBP
|
5,900,000
GBP
|
| Changes in equity [abstract] | |||||||||||||||||||||||||||||||||||
| Comprehensive income [abstract] | |||||||||||||||||||||||||||||||||||
| Profit (loss) | — | — |
—
GBP
|
— |
—
GBP
|
—
GBP
|
—
GBP
|
— |
—
GBP
|
— | — | — |
308,500,000
GBP
|
308,500,000
GBP
|
226,400,000
GBP
|
— | — |
—
GBP
|
226,400,000
GBP
|
—
GBP
|
— | — | — | — | — |
—
GBP
|
—
GBP
|
—
GBP
|
— | — | — | — | — | — | — |
| Other comprehensive income | — | — |
—
GBP
|
— |
—
GBP
|
8,500,000
GBP
|
—
GBP
|
— |
—
GBP
|
— | — | — |
8,500,000
GBP
|
—
GBP
|
3,300,000
GBP
|
— | — |
—
GBP
|
—
GBP
|
—
GBP
|
— | — | — | — | — |
—
GBP
|
3,300,000
GBP
|
—
GBP
|
— | — | — | — | — | — | — |
| Comprehensive income | — | — |
—
GBP
|
— |
—
GBP
|
8,500,000
GBP
|
—
GBP
|
— |
—
GBP
|
— | — | — |
317,000,000
GBP
|
308,500,000
GBP
|
223,100,000
GBP
|
— | — |
—
GBP
|
226,400,000
GBP
|
—
GBP
|
— | — | — | — | — |
—
GBP
|
3,300,000
GBP
|
—
GBP
|
— | — | — | — | — | — | — |
| Issue of equity | — | — |
1,013,000,000
GBP
|
— |
—
GBP
|
—
GBP
|
135,000,000
GBP
|
— |
2,200,000
GBP
|
— | — | — |
1,150,200,000
GBP
|
—
GBP
|
376,100,000
GBP
|
— | — |
374,900,000
GBP
|
—
GBP
|
—
GBP
|
— | — | — | — | — |
1,200,000
GBP
|
—
GBP
|
—
GBP
|
— | — | — | — | — | — | — |
| Increase (decrease) through share-based payment transactions, equity | — | — |
—
GBP
|
— |
13,600,000
GBP
|
—
GBP
|
—
GBP
|
— |
—
GBP
|
— | — | — |
71,100,000
GBP
|
57,500,000
GBP
|
48,300,000
GBP
|
— | — |
—
GBP
|
—
GBP
|
48,300,000
GBP
|
— | — | — | — | — |
—
GBP
|
—
GBP
|
—
GBP
|
— | — | — | — | — | — | — |