Reconciliation of Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) (USD $) In Millions, unless otherwise specified	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, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2011 Trading Securities [Member]	Sep. 30, 2012 Trading Securities [Member]	Jun. 30, 2012 Trading Securities [Member]	Dec. 31, 2011 Trading Securities [Member]	Jun. 30, 2011 Trading Securities [Member]	Sep. 30, 2012 Residential Mortgage		Sep. 30, 2011 Residential Mortgage		Sep. 30, 2012 Residential Mortgage		Sep. 30, 2011 Residential Mortgage		Sep. 30, 2012 Interest Rate Contract		Sep. 30, 2011 Interest Rate Contract		Sep. 30, 2012 Interest Rate Contract		Sep. 30, 2011 Interest Rate Contract		Sep. 30, 2012 Equity Contract		Sep. 30, 2011 Equity Contract		Sep. 30, 2012 Equity Contract		Sep. 30, 2011 Equity Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 315		$ 150		$ 130		$ 107		$ 6	$ 1	$ 1	$ 1	$ 1	$ 76		$ 59		$ 65		$ 46		$ 54	[1]	$ 5	[1]	$ 32	[1]	$ 2	[1]	$ 184	[1]	$ 85	[1]	$ 32	[1]	$ 53	[1]
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	147		89		395		158							1		3				4		163	[1]	100	[1]	338	[1]	154	[1]	(17)	[1]	(14)	[1]	57	[1]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liabilities Purchases			2																													2				2
Sales							5		5
Settlements	114		70		194		106							5		2		10		5		118	[1]	68	[1]	271	[1]	119	[1]	(9)	[1]			(87)	[1]	(18)	[1]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liabilities Level 3 Transfers Net	4	[2]	2	[2]	21	[2]	17	[2]						4	[2]	2	[2]	21	[2]	17	[2]
Ending balance	352		173		352		173		1	1	1	1	1	76		62		76		62		99	[1]	37	[1]	99	[1]	37	[1]	176	[1]	73	[1]	176	[1]	73	[1]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liabilities Change In Unrealized Gains Losses Relating To Assets	$ 85	[3]	$ 26	[3]	$ 230	[3]	$ 45	[3]						$ 1		$ 3	[3]			$ 4	[3]	$ 101	[3]	$ 37	[3]	$ 173	[1],[3]	$ 41	[1]	$ (17)	[3]	$ (14)	[3]	$ 57	[1],[3]

[1] Net interest rate derivatives include derivative assets and liabilities of $102 and $3, respectively, as of September 30, 2012 and $39 and $2, respectively, as of September 30, 2011. Net equity derivatives include derivative assets and liabilities of $198 and $22, respectively, as of September 30, 2012, and $103 and $30, respectively, as of September 30, 2011.

[2] Includes residential mortgage loans held for sale that were transferred to held for investment

[3] Includes interest income and expense.