Trade and Other Receivables - Summary of Trade and Other Receivables Reported in Balance Sheet Net of Allowances (Details) - GBP (£) £ in Millions |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Disclosure Of Trade And Other Receivables [Line Items] | ||
| Net trade and other receivables per balance sheet | £ 4,809 | £ 4,483 |
| Carrying Value | ||
| Disclosure Of Trade And Other Receivables [Line Items] | ||
| Net trade and other receivables per balance sheet | 4,894 | 4,570 |
| Allowance Account | ||
| Disclosure Of Trade And Other Receivables [Line Items] | ||
| Net trade and other receivables per balance sheet | £ (85) | £ (87) |