Derivative Instruments (Credit Derivatives Sold) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Derivative notional amount	$ 33,647	$ 58,640
Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	31,170	53,014
Total fair value of credit derivatives	(1,370)	(2,934)
Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Weighted average remaining expected maturity	2 years 8 months 12 days	5 years 1 month 6 days
Derivative notional amount	25,771	47,002
Total fair value of credit derivatives	(1,355)	(2,858)
Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Weighted average remaining expected maturity	19 years 1 month 6 days	19 years 4 months 24 days
Derivative notional amount	5,363	5,817
Total fair value of credit derivatives	(7)	(8)
Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Weighted average remaining expected maturity	28 years 3 months 18 days	1 year 9 months 18 days
Derivative notional amount	36	195
Total fair value of credit derivatives	(8)	(68)
Credit Rating Aaa [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	7,412	10,457
Total fair value of credit derivatives	(3)	(7)
Credit Rating Aaa [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	7,412	10,457
Credit Rating Aaa [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	0	0
Credit Rating Aaa [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount	0	0
Credit Rating Aa [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	3,227	5,965
Total fair value of credit derivatives	0	(70)
Credit Rating Aa [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	3,150	5,862
Credit Rating Aa [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	77	103
Credit Rating Aa [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount	0	0
Credit Rating A [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	5,399	8,914
Total fair value of credit derivatives	(6)	(72)
Credit Rating A [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	1,705	5,253
Credit Rating A [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	3,694	3,661
Credit Rating A [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount	0	0
Credit Rating Bbb [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	9,011	13,553
Total fair value of credit derivatives	(386)	(732)
Credit Rating Bbb [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	7,419	11,571
Credit Rating Bbb [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	1,592	1,982
Credit Rating Bbb [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount	0	0
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	6,121	14,125
Total fair value of credit derivatives	(975)	(2,053)
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	6,085	13,859
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	0	71
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount	$ 36	$ 195