Securities Available for Sale and Securities Held to Maturity - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012 CreditScore		Sep. 30, 2011		Sep. 30, 2012 CreditScore		Sep. 30, 2011		Dec. 31, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale Gross Unrealized Losses	$ 88				$ 88				$ 273
Fair Isaac & Company minimum credit score for Prime loan origination	620				620
Securities available for sale Amortized Cost	41,948				41,948				33,950
Securities available for sale	42,448				42,448				33,965
Cash and cash equivalents	8,523		6,376		8,523		6,376		8,679	4,931
Loan-to-deposit ratio	15.00%				15.00%
Net impairment losses on securities	3	[1]	13	[1]	28	[1]	22	[1]
Alt-A residential mortgage backed securities
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale Amortized Cost	326				326
Securities available for sale	$ 280				$ 280

[1] Net impairment losses on securities include total other-than-temporary impairment losses of $1 million and $2 million, net of $(2) million and $(11) million recognized in other comprehensive income, for the three months ended September 30, 2012 and 2011, respectively. Net impairment losses on securities include total other-than-temporary impairment losses of $15 million and $13 million, net of $(13) million and $(9) million recognized in other comprehensive income, for the nine months ended September 30, 2012 and 2011, respectively.