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, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale	$ 7,562	$ 7,957
Mortgage servicing rights	1,955	1,700	1,737	1,519
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	40,570	40,139
Mortgage loans held for sale	7,562	7,957
Mortgage servicing rights	1,955	1,700
Derivative assets	1,241	1,388
Other assets	899	480
Total	52,227	51,664
Derivative liabilities	667	634
Short-term borrowings	593	401
Total	1,260	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	1,506	1,226
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-backed Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	187	193
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	6,280	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	740	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	225	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	577	202
Fair Value, Measurements, Recurring [Member] | Residential [Member] | Residential Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	29,461	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	599	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	350	355
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	26	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	613	592
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,040	678
Other assets	134	94
Total	1,174	772
Short-term borrowings	88	50
Total	88	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	478	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	562	187
Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	38,532	38,458
Mortgage loans held for sale	7,562	7,957
Derivative assets	712	572
Other assets	765	386
Total	47,571	47,373
Derivative liabilities	2,081	2,128
Short-term borrowings	505	351
Total	2,586	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	1,028	735
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-backed Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	187	193
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	6,280	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	731	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	225	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	15	15
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Residential [Member] | Residential Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	29,461	29,495
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	26	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	573	577
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	998	1,003
Mortgage servicing rights	1,955	1,700
Derivative assets	1,044	1,234
Total	3,997	3,937
Derivative liabilities	58	55
Total	58	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	599	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	350	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 assets	(515)	(418)
Total	(515)	(418)
Derivative liabilities	(1,472)	(1,549)
Total	$ (1,472)	$ (1,549)