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	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Beginning balance	$ 437		$ 278		$ 130
Included in earnings	122		233		440
Purchases	(1)		(2)
Sales	(1)
Settlements	(102)		(106)		(318)
Transfers into Level 3	29	[1]	34	[1]	26	[1]
Ending balance	484		437		278
The amount of total gains or losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held	10	[2]	185	[2]	255	[2]
Trading Securities
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Beginning balance	1
Sales	(1)
Ending balance					1
Residential Mortgage
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Beginning balance	92		76		65
Included in earnings	4		(1)
Settlements	(17)		(17)		(15)
Transfers into Level 3	29	[1]	34	[1]	26	[1]
Ending balance	108		92		76
The amount of total gains or losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held	4	[2]	(1)	[2]
Interest Rate Contract
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Beginning balance	8	[3]	57	[3]	32	[3]
Included in earnings	125	[3]	59	[3]	418	[3]
Purchases	(1)	[3]	(2)	[3]
Settlements	(122)	[3]	(106)	[3]	(393)	[3]
Ending balance	10	[3]	8	[3]	57	[3]
The amount of total gains or losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held	13	[2],[3]	11	[2],[3]	233	[2],[3]
Equity Contract
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Beginning balance	336	[3]	144	[3]	32	[3]
Included in earnings	(7)	[3]	175	[3]	22	[3]
Settlements	37	[3]	17	[3]	90	[3]
Ending balance	366	[3]	336	[3]	144	[3]
The amount of total gains or losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held	$ (7)	[2],[3]	$ 175	[2],[3]	$ 22	[2],[3]

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

[2] Includes interest income and expense.

[3] Net interest rate derivatives include derivative assets and liabilities of $12 and $2, respectively, as of December 31, 2014, $12 and $4, respectively as of December 31, 2013 and $60 and $3, respectively, as of December 31, 2012. Net equity derivatives include derivative assets and liabilities of $415 and $49, respectively, as of December 31, 2014, $384 and $48, respectively, as of December 31, 2013, and $177 and $33, respectively, as of December 31, 2012.