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	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities before netting	$ 1,485		$ 1,598
Derivative liabilities netting	(1,138)		(1,192)
Derivative assets before netting	1,218		1,349
Derivative assets netting	(470)		(599)
Available-for-sale securities	44,761	[1]	40,935	[1]
Mortgage loans held for sale	1,827		3,263
Mortgage servicing rights	2,618		2,680		1,955	1,700
Mortgage-backed securities Residential [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	35,484		31,553
Commercial [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	144		152
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities total	425		525
Derivative assets total	814		805
Available-for-sale securities	44,761		40,935
Mortgage loans held for sale	1,827		3,263
Mortgage servicing rights	2,618		2,680
Other assets	974		731
Total	50,994		48,414
Short-term borrowings	674		663
Total	1,099		1,188
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	1,062		1,045
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	5,585		5,738
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	670		640
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	218		212
Fair Value, Measurements, Recurring [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	178		161
Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Non-agency Prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	465		478
Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Non-agency Non-prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	297		297
Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	35,484		31,553
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	144		152
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	628		629
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	24		24
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	166		148
Mortgage loans held for sale
Mortgage servicing rights
Other assets	118		143
Total	284		291
Short-term borrowings	75		112
Total	75		112
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	7		7
Level 1 [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
Level 1 [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
Level 1 [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
Level 1 [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
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	159		141
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Non-agency Prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Non-agency Non-prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Level 1 [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
Level 1 [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
Level 1 [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
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	1,503		1,647
Derivative assets before netting	742		889
Available-for-sale securities	43,759		39,940
Mortgage loans held for sale	1,827		3,263
Mortgage servicing rights	0
Other assets	856		588
Total	47,184		44,680
Short-term borrowings	599		551
Total	2,102		2,198
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	1,055		1,038
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	5,585		5,738
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	661		631
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	218		212
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	19		20
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Non-agency Prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Non-agency Non-prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	35,484		31,553
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	144		152
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	563		566
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	24		24
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	60		70
Derivative assets before netting	542		515
Available-for-sale securities	836		847
Mortgage loans held for sale
Mortgage servicing rights	2,618		2,680
Other assets
Total	3,996		4,042
Short-term borrowings
Total	60		70
Level 3 [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
Level 3 [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
Level 3 [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
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] | Perpetual preferred securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Non-agency Prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	465		478
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Non-agency Non-prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	297		297
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Level 3 [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
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	65		63
Level 3 [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
Netting [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities netting	(1,138)		(1,192)
Derivative assets netting	(470)		(599)
Available-for-sale securities
Mortgage loans held for sale
Mortgage servicing rights
Other assets
Total	(470)		(599)
Short-term borrowings
Total	(1,138)		(1,192)
Netting [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
Netting [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
Netting [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
Netting [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
Netting [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
Netting [Member] | Fair Value, Measurements, Recurring [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Netting [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Non-agency Prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Netting [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Non-agency Non-prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Netting [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities Residential [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Netting [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
Netting [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
Netting [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

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