Statement Of Comprehensive Income [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 |
|---|---|---|---|---|---|---|---|---|
| Statement of comprehensive income [abstract] | ||||||||
| Profit (loss) | — | — |
442,800,000
GBP
|
442,800,000
GBP
|
430,000,000
GBP
|
430,000,000
GBP
|
— | — |
| Other comprehensive income [abstract] | ||||||||
| Components of other comprehensive income that will not be reclassified to profit or loss, before tax [abstract] | ||||||||
| Other comprehensive income, before tax, gains (losses) on remeasurements of defined benefit plans | — | — |
74,100,000
GBP
|
74,100,000
GBP
|
16,200,000
GBP
|
16,200,000
GBP
|
— | — |
| Components of other comprehensive income that will be reclassified to profit or loss, before tax [abstract] | ||||||||
| Exchange differences on translation [abstract] | ||||||||
| Other comprehensive income, before tax, exchange differences on translation of foreign operations | — |
89,800,000
GBP
|
89,800,000
GBP
|
— | — |
63,500,000
GBP
|
63,500,000
GBP
|
— |
| Hedges of net investment in foreign operations [abstract] | ||||||||
| Other comprehensive income, before tax, hedges of net investments in foreign operations | — |
11,500,000
GBP
|
11,500,000
GBP
|
— | — |
15,900,000
GBP
|
15,900,000
GBP
|
— |
| Income tax relating to components of other comprehensive income that will not be reclassified to profit or loss [abstract] | ||||||||
| Income tax relating to components of other comprehensive income that will not be reclassified to profit or loss | — | — |
19,300,000
GBP
|
— | — |
4,600,000
GBP
|
— | — |
| Income tax relating to components of other comprehensive income that will be reclassified to profit or loss [abstract] | ||||||||
| Income tax relating to components of other comprehensive income that will be reclassified to profit or loss | — | — |
–
GBP
|
— | — |
300,000
GBP
|
— | — |
| Other comprehensive income | — | — |
19,100,000
GBP
|
— | — |
99,200,000
GBP
|
— | — |
| Comprehensive income |
3,600,000
GBP
|
78,300,000
GBP
|
423,700,000
GBP
|
498,400,000
GBP
|
416,800,000
GBP
|
330,800,000
GBP
|
79,100,000
GBP
|
6,900,000
GBP
|
| Comprehensive income attributable to [abstract] | ||||||||
| Comprehensive income, attributable to owners of parent | — | — |
423,700,000
GBP
|
— | — |
330,800,000
GBP
|
— | — |