Insurance Premiums (Narrative) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Insurance Premiums [Line Items]
Premiums receivable		$ 216	$ 249	$ 296
Weighted average risk-free rate		2.70%	2.80%
Weighted average expected collection term of the premiums receivable, years		8 years 9 months	8 years 10 months 9 days
Reinsurance premiums payable	[1]	$ 38
Premiums [Member]
Insurance Premiums [Line Items]
Premiums receivable		5
Reinsurance premiums payable		$ 15	$ 17

[1] Total reinsurance recoverable/(payable) is primarily related to recoverables on unpaid losses net of (payables) on salvage received.