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Deferred tax - Analysis of Deferred Tax Balances for Financial Reporting Purposes (Detail) - GBP (£)
£ in Millions
Dec. 31, 2019
Dec. 31, 2018
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Deferred tax assets gross £ 430.9 £ 412.0
Deferred tax assets, offset (243.0) (259.0)
Deferred tax assets 187.9 153.0
Deferred tax liabilities gross (622.8) (738.5)
Deferred tax liabilities, offset 243.0 259.0
Deferred tax liabilities (379.8) (479.5)
Deferred tax assets (liabilities) £ (191.9) £ (326.5)