Derivative Instruments (Credit Derivatives Sold) (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
Insured Swaps [Member]
Derivative [Line Items]
Weighted average remaining expected maturity	13 years 8 months 12 days	13 years 8 months 12 days
Insurance Operations [Member]
Derivative [Line Items]
Total fair value of credit derivatives	$ 0	$ 0
Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	1,328	1,350
Total fair value of credit derivatives	0	0
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	48	50
Credit Rating A [Member] | Insurance Operations [Member]
Derivative [Line Items]
Total fair value of credit derivatives	0	0
Credit Rating A [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	1,010	1,013
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	210	227
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member]
Derivative [Line Items]
Total fair value of credit derivatives	0	0
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	$ 60	$ 60