Debt - Senior Unsecured Notes - Additional Information (Detail)	Mar. 24, 2021 GBP (£)
Unsecured Debt
Debt Instrument [Line Items]
Senior unsecured notes face amount	£ 850,000,000

Face (par) amount of debt instrument at time of issuance.

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Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant