Reconciliation of Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) (USD $) In Millions	3 Months Ended		9 Months Ended						3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 Trading Securities [Member]	Sep. 30, 2010 Trading Securities [Member]	Jun. 30, 2011 Trading Securities [Member]	Jun. 30, 2010 Trading Securities [Member]	Sep. 30, 2011 Residential Mortgage	Sep. 30, 2010 Residential Mortgage	Sep. 30, 2011 Residential Mortgage	Sep. 30, 2010 Residential Mortgage	Sep. 30, 2011 Interest Rate Contract	Sep. 30, 2010 Interest Rate Contract	Sep. 30, 2011 Interest Rate Contract	Sep. 30, 2010 Interest Rate Contract	Sep. 30, 2011 Equity Contract	Sep. 30, 2010 Equity Contract	Sep. 30, 2011 Equity Contract	Sep. 30, 2010 Equity Contract	Sep. 30, 2010 Retained Interest
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 150	$ 100	$ 107	$ 222	$ 6	$ 13	$ 1	$ 5	$ 59	$ 41	$ 46	$ 26	$ 5	$ 24	$ 2	$ (2)	$ 85	$ 30	$ 53	$ 11	$ 174
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liabilities Included In Earnings	89	92	158	202		3			3		4		100	102	154	210	(14)	(10)		(11)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liabilities Purchases Sales Issuances Settlements Maturities Paydowns Net		(91)		(338)		(11)				(2)		(2)		(89)		(171)				20	(174)
Sales			(5)		(5)
Settlements	(70)		(106)						(2)		(5)		(68)		(119)				18
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liabilities Level 3 Transfers Net	2	3	17	18					2	3	17	18
Ending balance	173	104	173	104	1	5	1	5	62	42	62	42	37	37	37	37	73	20	73	20
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liabilities Change In Unrealized Gains Losses Relating To Assets	$ 26	$ 25	$ 45	$ 50					$ 3		$ 4		$ 37	$ 35	$ 41	$ 61	$ (14)	$ (10)		$ (11)