Debt - Debt Maturities, Assuming the Exercise of all Extensions that are Exercisable Solely at our Option (Parenthetical) (Detail) $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($)
Debt Disclosure [Abstract]
Outstanding balance	$ 96
Extension period	2 years

Average amount borrowed under the credit facility during the period.

No definition available.

Name:	us-gaap_LineOfCreditFacilityAverageOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration