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, 2014		Mar. 31, 2014	Dec. 31, 2013		Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities before netting	$ 1,432			$ 1,598
Derivative liabilities netting	(1,127)			(1,192)
Derivative assets before netting	1,167			1,349
Derivative assets netting	(411)			(599)
Available-for-sale securities	48,389	[1]		40,935	[1]
Mortgage loans held for sale	2,994			3,263
Mortgage servicing rights	2,412		2,618	2,680		2,377	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	38,292			31,553
Commercial [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	133			152
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities total	494			525
Derivative assets total	935			805
Available-for-sale securities	48,389			40,935
Mortgage loans held for sale	2,994			3,263
Mortgage servicing rights	2,412			2,680
Other assets	916			731
Total	55,646			48,414
Short-term borrowings	672			663
Total	1,166			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	1,870			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	5,598			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	629			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	224			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	256			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	447			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	286			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	38,292			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	133			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	625			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	23			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	992			148
Mortgage loans held for sale
Mortgage servicing rights
Other assets	99			143
Total	1,091			291
Short-term borrowings	214			112
Total	214			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	755			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	237			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	1,541			1,647
Derivative assets before netting	708			889
Available-for-sale securities	46,589			39,940
Mortgage loans held for sale	2,994			3,263
Mortgage servicing rights
Other assets	817			588
Total	51,108			44,680
Short-term borrowings	458			551
Total	1,999			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	1,115			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	5,598			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	620			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	224			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	38,292			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	133			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	559			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	23			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	80			70
Derivative assets before netting	638			515
Available-for-sale securities	808			847
Mortgage loans held for sale
Mortgage servicing rights	2,412			2,680
Other assets
Total	3,858			4,042
Short-term borrowings
Total	80			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	447			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	286			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	66			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	(1,127)			(1,192)
Derivative assets netting	(411)			(599)
Available-for-sale securities
Mortgage loans held for sale
Mortgage servicing rights
Other assets
Total	(411)			(599)
Short-term borrowings
Total	(1,127)			(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.