Balances of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Jun. 30, 2012	Dec. 31, 2011		Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights	$ 1,553		$ 1,594	$ 1,519		$ 1,466	$ 1,989	$ 1,837
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	39,636			51,937
Mortgage loans held for sale	9,815			6,925
Mortgage servicing rights	1,553			1,519
Derivative assets	1,822			1,619
Other assets	733			613
Total	53,559			62,613
Derivative liabilities	953			665
Other liabilities	592			613
Total	1,545			1,278
Fair Value, Measurements, Recurring | U.S. Treasury and agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	743			1,057
Fair Value, Measurements, Recurring | Commercial Mortgage-backed Agency Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	202			140	[1]
Fair Value, Measurements, Recurring | Obligations of state and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	6,457			6,539
Fair Value, Measurements, Recurring | Obligations of foreign governments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	6			6
Fair Value, Measurements, Recurring | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	709			827
Fair Value, Measurements, Recurring | Perpetual preferred securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	278			318
Fair Value, Measurements, Recurring | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	268			202
Fair Value, Measurements, Recurring | Residential | Residential Agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	29,362			40,314
Fair Value, Measurements, Recurring | Residential | Residential non-agency prime
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	631	[2]		803
Fair Value, Measurements, Recurring | Residential | Residential non-agency non-prime
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	340	[1]		802	[2]
Fair Value, Measurements, Recurring | Asset-Backed Securities | Collateralized Loan Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	42			206
Fair Value, Measurements, Recurring | Asset-Backed Securities | Asset Backed Securities Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	598			681
Fair Value, Measurements, Recurring | Commercial Mortgage-Backed Securities | Non-agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities				42
Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	760			755
Other assets	179			146
Total	939			901
Other liabilities	39			75
Total	39			75
Level 1 | Fair Value, Measurements, Recurring | U.S. Treasury and agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	504			562
Level 1 | Fair Value, Measurements, Recurring | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	256			193
Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	37,880			49,289
Mortgage loans held for sale	9,815			6,925
Derivative assets	637			632
Other assets	554			467
Total	48,886			57,313
Derivative liabilities	2,591			2,501
Other liabilities	553			538
Total	3,144			3,039
Level 2 | Fair Value, Measurements, Recurring | U.S. Treasury and agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	239			495
Level 2 | Fair Value, Measurements, Recurring | Commercial Mortgage-backed Agency Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	202			140	[1]
Level 2 | Fair Value, Measurements, Recurring | Obligations of state and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	6,457			6,539
Level 2 | Fair Value, Measurements, Recurring | Obligations of foreign governments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	6			6
Level 2 | Fair Value, Measurements, Recurring | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	700			818
Level 2 | Fair Value, Measurements, Recurring | Perpetual preferred securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	278			318
Level 2 | Fair Value, Measurements, Recurring | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	12			9
Level 2 | Fair Value, Measurements, Recurring | Residential | Residential Agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	29,362			40,314
Level 2 | Fair Value, Measurements, Recurring | Asset-Backed Securities | Collateralized Loan Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	42			86
Level 2 | Fair Value, Measurements, Recurring | Asset-Backed Securities | Asset Backed Securities Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	582			564
Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	996			1,893
Mortgage servicing rights	1,553			1,519
Derivative assets	1,539			1,281
Total	4,088			4,693
Derivative liabilities	49			53
Total	49			53
Level 3 | Fair Value, Measurements, Recurring | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	9			9
Level 3 | Fair Value, Measurements, Recurring | Residential | Residential non-agency prime
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	631	[2]		803
Level 3 | Fair Value, Measurements, Recurring | Residential | Residential non-agency non-prime
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	340	[1]		802	[2]
Level 3 | Fair Value, Measurements, Recurring | Asset-Backed Securities | Collateralized Loan Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities				120
Level 3 | Fair Value, Measurements, Recurring | Asset-Backed Securities | Asset Backed Securities Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	16			117
Level 3 | Fair Value, Measurements, Recurring | Commercial Mortgage-Backed Securities | Non-agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities				42
Netting | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	(354)			(294)
Total	(354)			(294)
Derivative liabilities	(1,687)			(1,889)
Total	$ (1,687)			$ (1,889)

[1] Includes all securities not meeting the conditions to be designated as prime.

[2] Prime securities are those designated as such by the issuer at origination. When an issuer designation is unavailable, the Company determines at acquisition date the categorization based on asset pool characteristics (such as weighted-average credit score, loan-to-value, loan type, prevalence of low documentation loans) and deal performance (such as pool delinquencies and security market spreads).