Derivative Instruments (Credit Derivatives Sold) (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Insured Swaps [Member]
Derivative [Line Items]
Weighted average remaining expected maturity	14 years	14 years 1 month 6 days
Insurance Operations [Member]
Derivative [Line Items]
Total fair value of credit derivatives	$ (1)	$ (1)
Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	1,473	1,489
Total fair value of credit derivatives	(1)	(1)
Credit Rating Aaa [Member] | Insurance Operations [Member]
Derivative [Line Items]
Total fair value of credit derivatives	0	0
Credit Rating Aaa [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	0	0
Credit Rating Aa [Member] | Insurance Operations [Member]
Derivative [Line Items]
Total fair value of credit derivatives	0	0
Credit Rating Aa [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	59	61
Credit Rating A [Member] | Insurance Operations [Member]
Derivative [Line Items]
Total fair value of credit derivatives	(1)	(1)
Credit Rating A [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	1,122	1,136
Credit Rating Bbb [Member] | Insurance Operations [Member]
Derivative [Line Items]
Total fair value of credit derivatives	0	0
Credit Rating Bbb [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	292	292
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member]
Derivative [Line Items]
Total fair value of credit derivatives		0
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	$ 0	$ 0