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	Sep. 30, 2013		Jun. 30, 2013	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities before netting	$ 1,825			$ 2,178
Derivative liabilities netting	(1,358)			(1,549)
Derivative assets before netting	1,362			1,546
Derivative assets netting	(572)			(418)
Available-for-sale securities	39,307	[1]		40,139	[1]
Mortgage loans held for sale	3,844			7,957
Mortgage servicing rights	2,577		2,377	1,700		1,553	1,594	1,519
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities total	522			634
Derivative assets total	973			1,388
Available-for-sale securities	39,307			40,139
Mortgage loans held for sale	3,844			7,957
Mortgage servicing rights	2,577			1,700
Other assets	1,007			480
Total	47,708			51,664
Short-term borrowings	764			401
Total	1,286			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	1,521			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	5,820			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	642			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	209			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	282			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	29,220			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	500			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	303			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	169			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	610			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	728			678
Mortgage loans held for sale
Mortgage servicing rights
Other assets	85			94
Total	813			772
Short-term borrowings	231			50
Total	231			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	463			491
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 investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	265			187
Level 1 [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
Level 1 [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
Level 1 [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
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] | Collateralized Loan Obligations [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 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities before netting	1,827			2,128
Derivative assets before netting	875			572
Available-for-sale securities	37,727			38,458
Mortgage loans held for sale	3,844			7,957
Mortgage servicing rights
Other assets	922			386
Total	43,368			47,373
Short-term borrowings	533			351
Total	2,360			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	1,058			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	5,820			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	633			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	209			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	17			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	29,220			29,495
Level 2 [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
Level 2 [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
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	169			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	570			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	53			55
Derivative assets before netting	670			1,234
Available-for-sale securities	852			1,003
Mortgage loans held for sale
Mortgage servicing rights	2,577			1,700
Other assets
Total	4,099			3,937
Short-term borrowings
Total	53			55
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 investments [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] | 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] | Residential [Member] | Residential Non-Agency Prime [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	500			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	303			355
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] | Collateralized Loan Obligations [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	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	(1,358)			(1,549)
Derivative assets netting	(572)			(418)
Available-for-sale securities
Mortgage loans held for sale
Mortgage servicing rights
Other assets
Total	(572)			(418)
Short-term borrowings
Total	(1,358)			(1,549)
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 investments [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] | 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] | Residential [Member] | Residential 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] | 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
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] | 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] | 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

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