Fair Values of Assets and Liabilities - Balances of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Mar. 31, 2013	Dec. 31, 2012		Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities before netting	$ 1,956			$ 2,178
Derivative liabilities netting	(1,293)			(1,549)
Derivative assets before netting	2,035			1,546
Derivative assets netting	(612)			(418)
Available-for-sale securities	40,307	[1]		40,139	[1]
Mortgage loans held for sale	4,753			7,957
Mortgage servicing rights	2,377		1,955	1,700		1,594	1,737	1,519
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities total	938			634
Derivative assets total	1,461			1,388
Available-for-sale securities	40,307			40,139
Mortgage loans held for sale	4,753			7,957
Mortgage servicing rights	2,377			1,700
Other assets	887			480
Total	49,785			51,664
Short-term borrowings	697			401
Total	1,635			1,035
Fair Value, Measurements, Recurring [Member] | U.S. Treasury and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,551			1,226
Fair Value, Measurements, Recurring [Member] | Obligations of state and political subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	5,945			6,455
Fair Value, Measurements, Recurring [Member] | Obligations of foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	6			6
Fair Value, Measurements, Recurring [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	707			731
Fair Value, Measurements, Recurring [Member] | Perpetual preferred securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	219			218
Fair Value, Measurements, Recurring [Member] | Other investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	243			202
Fair Value, Measurements, Recurring [Member] | Residential [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	29,956			29,495
Fair Value, Measurements, Recurring [Member] | Residential [Member] | Residential Non-Agency Prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	547			624
Fair Value, Measurements, Recurring [Member] | Residential [Member] | Residential Non-Agency Non-Prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	319			355
Fair Value, Measurements, Recurring [Member] | Commercial [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	177			193
Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member] | Collateralized Loan Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	25			42
Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member] | Asset Backed Securities Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	612			592
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities before netting
Derivative assets before netting
Available-for-sale securities	696			678
Other assets	107			94
Total	803			772
Short-term borrowings	135			50
Total	135			50
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasury and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	469			491
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	227			187
Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities before netting	2,025			2,128
Derivative assets before netting	1,444			572
Available-for-sale securities	38,696			38,458
Mortgage loans held for sale	4,753			7,957
Other assets	780			386
Total	45,673			47,373
Short-term borrowings	562			351
Total	2,587			2,479
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasury and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,082			735
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Obligations of state and political subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	5,945			6,455
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Obligations of foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	6			6
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	698			722
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Perpetual preferred securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	219			218
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	16			15
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Residential [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	29,956			29,495
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	177			193
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member] | Collateralized Loan Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	25			42
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member] | Asset Backed Securities Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	572			577
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities before netting	206			55
Derivative assets before netting	629			1,234
Available-for-sale securities	915			1,003
Mortgage servicing rights	2,377			1,700
Total	3,921			3,937
Total	206			55
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	9			9
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Residential [Member] | Residential Non-Agency Prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	547			624
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Residential [Member] | Residential Non-Agency Non-Prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	319			355
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member] | Asset Backed Securities Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	40			15
Netting [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities netting	(1,293)			(1,549)
Derivative assets netting	(612)			(418)
Total	(612)			(418)
Total	$ (1,293)			$ (1,549)

[1] Includes only collateral pledged by the Company where counterparties have the right to sell or pledge the collateral.