Derivative Instruments (Credit Derivatives Sold) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Credit Default Swap [Member]
Derivative [Line Items]
Weighted average remaining expected maturity	3 years 11 months	2 years 1 month
Insured Swaps [Member]
Derivative [Line Items]
Weighted average remaining expected maturity	15 years 6 months	16 years 6 months
Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	$ 4,043	$ 6,994
Total fair value of credit derivatives	(66)	(88)
Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	588	3,208
Total fair value of credit derivatives	(64)	(85)
Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	3,035	3,786
Total fair value of credit derivatives	$ (2)	(3)
Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Total fair value of credit derivatives		0
Insurance Operations [Member] | Insured Swaps - Held for Sale [Member]
Derivative [Line Items]
Weighted average remaining expected maturity	14 years 2 months
Derivative notional amount	$ 420
Credit Rating Aaa [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	0	1,947
Total fair value of credit derivatives		0
Credit Rating Aaa [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	0	1,947
Credit Rating Aaa [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount		0
Credit Rating Aaa [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount		0
Credit Rating Aa [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	137	109
Total fair value of credit derivatives		0
Credit Rating Aa [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount		0
Credit Rating Aa [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	137	109
Credit Rating Aa [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount		0
Credit Rating A [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	2,261	3,015
Total fair value of credit derivatives	(1)	(4)
Credit Rating A [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	115	300
Credit Rating A [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	2,146	2,715
Credit Rating A [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount		0
Credit Rating Bbb [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	1,152	940
Total fair value of credit derivatives	(1)	(2)
Credit Rating Bbb [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount		0
Credit Rating Bbb [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	732	940
Credit Rating Bbb [Member] | Insurance Operations [Member] | Insured Swaps - Held for Sale [Member]
Derivative [Line Items]
Derivative notional amount	420
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	493	983
Total fair value of credit derivatives	(64)	(82)
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	473	961
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	$ 20	22
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount		$ 0