Variable Interest Entities (Narrative) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Variable Interest Entity [Line Items]
Carrying amounts of assets	$ 4,696	$ 5,751
Carrying amounts of liabilities	4,996	5,602
Variable Interest Entity Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Carrying amounts of assets	169	830
Carrying amounts of liabilities	$ 291	$ 623
Variable Interest Entity Primary Beneficiary [Member] | U S Public Finance Insurance [Member]
Variable Interest Entity [Line Items]
Number of variable interest entities deconsolidated		7
Variable Interest Entity Primary Beneficiary [Member] | Structured Finance And International Insurance [Member]
Variable Interest Entity [Line Items]
Number of variable interest entities deconsolidated	3	2
Variable Interest Entity Primary Beneficiary [Member] | Structured Finance And International Insurance [Member] | Recorded Due To Credit Losses In AOCI [Member]
Variable Interest Entity [Line Items]
Net realized gains (losses) related to the initial consolidation	$ (14)