Fair Values of Assets and Liabilities - Balances of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities netting		$ (1,652)	$ (1,283)
Derivative liabilities total		484	526
Derivative assets netting		(1,071)	(807)
Derivative assets total		1,414	1,072
Available-for-sale securities	[1]	64,912	61,997
Mortgage loans held for sale		3,993	3,110
Mortgage servicing rights		2,222	2,512	$ 2,250	$ 2,338
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities total		2,017	1,102
Derivative assets total		2,545	1,440
Available-for-sale securities		64,912	61,997
Mortgage loans held for sale		3,993	3,110
Mortgage servicing rights		2,222	2,512
Other assets		930	791
Total		74,602	69,850
Short-term borrowings		810	767
Total		2,827	1,869
Fair Value, Measurements, Recurring [Member] | Netting and Collateral One [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities netting		(1,652)	(1,283)
Derivative assets netting		(1,071)	(807)
Total		(1,071)	(807)
Total		(1,652)	(1,283)
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		7,769	4,596
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		5,197	5,316
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		586	610
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		142	161
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		60	68
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		297	318
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		227	240
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		50,051	50,076
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		32	52
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		18	19
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		533	541
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			2
Derivative assets before netting		2
Available-for-sale securities		7,071	3,898
Other assets		173	202
Total		7,246	4,100
Short-term borrowings		144	122
Total		144	124
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		6,887	3,708
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		103	102
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		48	48
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		33	40
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		3,524	2,266
Derivative assets before netting		2,617	1,632
Available-for-sale securities		57,306	57,530
Mortgage loans held for sale		3,993	3,110
Other assets		757	589
Total		64,673	62,861
Short-term borrowings		666	645
Total		4,190	2,911
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		882	888
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		5,197	5,316
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		474	499
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		94	113
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		27	28
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		50,051	50,076
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		32	52
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		18	19
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		531	539
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		145	117
Derivative assets before netting		997	615
Available-for-sale securities		535	569
Mortgage servicing rights		2,222	2,512
Total		3,754	3,696
Total		145	117
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] | 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		297	318
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		227	240
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		$ 2	$ 2

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