Fair Value Measurement and Fair Value of Financial Instruments - Reconciliation of Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Detail) (Fair Value Measurements Recurring [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Reconciliation of asset balance at fair value on a recurring basis using significant unobservable inputs, beginning of period	$ 186	$ 153	$ 136
Included in income before taxes	(5)	(34)	42	(34)
Purchases/additions, assets	1	2	4	2
Transfers into Level 3, assets				153
Sales		(3)		(3)
Reconciliation of asset balance at fair value on a recurring basis using significant unobservable inputs, end of period	182	118	182	118
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	(5)	(34)	42	(34)
Securities Available for Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Reconciliation of asset balance at fair value on a recurring basis using significant unobservable inputs, beginning of period	1,592	43	1,499	48
Included in other comprehensive income	18	1	37	(4)
Purchases/additions, assets	192	1,090	329	1,090
Sales			(14)
Settlements	(40)		(89)
Reconciliation of asset balance at fair value on a recurring basis using significant unobservable inputs, end of period	1,762	1,134	1,762	1,134
Other assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Reconciliation of asset balance at fair value on a recurring basis using significant unobservable inputs, beginning of period	1
Included in income before taxes	1		1
Purchases/additions, assets			1
Reconciliation of asset balance at fair value on a recurring basis using significant unobservable inputs, end of period	2		2
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	1		1
Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Reconciliation of liability balance at fair value on a recurring basis using significant unobservable inputs, beginning of period	(187)	(153)	(136)
Included in income before taxes	5	34	(43)	34
Purchases/additions, liability		(2)		(2)
Transfers into Level 3, liability				(153)
Sales	(1)	3	(4)	3
Reconciliation of liability balance at fair value on a recurring basis using significant unobservable inputs, ending of period	(183)	(118)	(183)	(118)
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	5	(34)	(43)	34
Other Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Reconciliation of liability balance at fair value on a recurring basis using significant unobservable inputs, beginning of period	(96)	(63)	(95)	(51)
Included in income before taxes	2	(9)	1	(21)
Reconciliation of liability balance at fair value on a recurring basis using significant unobservable inputs, ending of period	(94)	(72)	(94)	(72)
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	$ 2	$ (9)	$ 1	$ (21)