Fair Values of Assets and Liabilities - Balances of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions		Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities netting		$ (1,869)		$ (1,283)
Derivative liabilities total		578		526
Derivative assets netting		(1,130)		(807)
Derivative assets total		1,752		1,072
Available-for-sale securities	[1]	66,490		61,997
Mortgage loans held for sale		4,309		3,110
Mortgage servicing rights		2,056	$ 2,222	2,512	$ 2,481	$ 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		2,735		1,102
Derivative assets total		3,382		1,440
Available-for-sale securities		66,490		61,997
Mortgage loans held for sale		4,309		3,110
Mortgage servicing rights		2,056		2,512
Other assets		1,000		791
Total		77,237		69,850
Short-term borrowings		788		767
Total		3,523		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		(1,869)		(1,283)
Derivative assets netting		(1,130)		(807)
Total		(1,130)		(807)
Total		(1,869)		(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		11,612		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		5,423		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		608		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		72		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		66		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		280		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		216		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		47,647		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		20		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		16		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		530		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		4
Available-for-sale securities		10,902		3,898
Other assets		145		202
Total		11,051		4,100
Short-term borrowings		171		122
Total		171		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		10,733		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		102		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		28		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		39		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		4,388		2,266
Derivative assets before netting		3,212		1,632
Available-for-sale securities		55,081		57,530
Mortgage loans held for sale		4,309		3,110
Other assets		855		589
Total		63,457		62,861
Short-term borrowings		617		645
Total		5,005		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		879		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		5,423		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		497		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		44		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		47,647		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		20		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		16		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		528		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		216		117
Derivative assets before netting		1,296		615
Available-for-sale securities		507		569
Mortgage servicing rights		2,056		2,512
Total		3,859		3,696
Total		216		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		280		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		216		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.