Summary of Other than Temporary Impairment by Investment Category (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other Gains (losses)	$ (2)		$ 2		$ (3)		$ 17
Available-for-sale Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Losses Recorded in Earnings	(15)		(9)		(64)		(24)
Other Gains (losses)	2	[1]	(2)	[1]	3	[1]	(17)	[1]
Total Available for sale other-than-temporary impairment	(13)		(11)		(61)		(41)
Residential non-agency prime | Available-for-sale Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Losses Recorded in Earnings	(5)	[2]			(8)	[2]	(2)	[2]
Other Gains (losses)	(3)	[1],[2]			(12)	[1],[2]	(3)	[1],[2]
Total Available for sale other-than-temporary impairment	(8)	[2]			(20)	[2]	(5)	[2]
Residential non-agency non-prime | Available-for-sale Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Losses Recorded in Earnings	(10)	[3]	(6)	[3]	(27)	[3]	(18)	[3]
Other Gains (losses)	5	[1],[3]	(4)	[1],[3]	15	[1],[3]	(16)	[1],[3]
Total Available for sale other-than-temporary impairment	(5)	[3]	(10)	[3]	(12)	[3]	(34)	[3]
Other asset-backed securities | Available-for-sale Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Losses Recorded in Earnings			(3)		(1)		(4)
Other Gains (losses)			2	[1]	1	[1]	2	[1]
Total Available for sale other-than-temporary impairment			(1)				(2)
Commercial Mortgage-Backed Securities | Non-agency | Available-for-sale Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Losses Recorded in Earnings					(1)
Other Gains (losses)					(1)	[1]
Total Available for sale other-than-temporary impairment					(2)
Perpetual preferred securities | Available-for-sale Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Losses Recorded in Earnings					(27)
Total Available for sale other-than-temporary impairment					$ (27)

[1] Losses represent the non-credit portion of other-than-temporary impairment recorded in other comprehensive income for investment securities determined to be other-than-temporarily impaired during the period. Gains represent recoveries in the fair value of securities that have or previously had non-credit other-than-temporary impairment.

[2] Prime securities are those designated as such by the issuer at origination. When an issuer designation is unavailable, the Company determines at acquisition date the categorization based on asset pool characteristics (such as weighted-average credit score, loan-to-value, loan type, prevalence of low documentation loans) and deal performance (such as pool delinquencies and security market spreads).

[3] Includes all securities not meeting the conditions to be designated as prime.