Fair Value Measurement and Fair Value of Financial Instruments (Details) - USD ($) $ in Millions		Mar. 31, 2016		Dec. 31, 2015
Fair value measurements
Trading account assets		$ 1,370		$ 1,087
Securities available for sale		13,003
U.S. Treasury
Fair value measurements
Securities available for sale		152
Residential mortgage-backed securities, U.S. government agency and government-sponsored agencies
Fair value measurements
Securities available for sale		6,308
Residential mortgage-backed securities, Privately issued
Fair value measurements
Securities available for sale		203
Collateralized loan obligations
Fair value measurements
Securities available for sale		3,227
Other Asset Liability Management Securities
Fair value measurements
Securities available for sale		7
Other debt securities, Direct bank purchase bonds
Fair value measurements
Securities available for sale		1,581
Other debt securities, Other
Fair value measurements
Securities available for sale		33
Level 3
Fair value measurements
Other assets				17
Fair Value, Measurements, Recurring [Member]
Fair value measurements
Trading account assets		(834)	[1]	(834)	[2]
Other assets		(208)	[1]	(75)	[2]
Total assets		$ (1,042)	[1]	(909)	[2]
Percentage of Total		100.00%
Percentage of Total Company Assets		12.00%
Trading account liabilities		$ (1,266)	[1]	(858)	[2]
Other liabilities		0		(14)	[2]
Total liabilities		$ (1,266)	[1]	(872)	[2]
Percentage of Total		100.00%
Percentage of Total Company Liabilities		1.00%
Fair Value, Measurements, Recurring [Member] | Level 1
Fair value measurements
Trading account assets		$ 2		1
Securities available for sale		8		8
Total assets		$ 10		$ 9
Percentage of Total		0.00%		0.00%
Percentage of Total Company Assets		0.00%		0.00%
Trading account liabilities		$ 3		$ 2
Total liabilities		$ 3		$ 2
Percentage of Total		0.00%		0.00%
Percentage of Total Company Liabilities		0.00%		0.00%
Fair Value, Measurements, Recurring [Member] | Level 1 | Interest rate derivative contracts
Fair value measurements
Trading account assets		$ 1		$ 0
Trading account liabilities		3		1
Fair Value, Measurements, Recurring [Member] | Level 1 | Foreign exchange derivative contracts
Fair value measurements
Trading account assets		1		1
Trading account liabilities		0		1
Fair Value, Measurements, Recurring [Member] | Level 1 | Equity securities
Fair value measurements
Securities available for sale		8		8
Fair Value, Measurements, Recurring [Member] | Level 2
Fair value measurements
Trading account assets		2,013		1,692
Securities available for sale		11,390		12,733
Other assets		274		77
Total assets		$ 13,677		$ 14,502
Percentage of Total		94.00%		94.00%
Percentage of Total Company Assets		11.00%		12.00%
Trading account liabilities		$ 1,823		$ 1,429
Other liabilities		1		14
Total liabilities		$ 1,824		$ 1,443
Percentage of Total		211.00%		159.00%
Percentage of Total Company Liabilities		2.00%		1.00%
Fair Value, Measurements, Recurring [Member] | Level 2 | U.S. Treasury
Fair value measurements
Trading account assets		$ 36		$ 37
Securities available for sale		152		594
Fair Value, Measurements, Recurring [Member] | Level 2 | U.S. government-sponsored agencies
Fair value measurements
Trading account assets		97		106
Fair Value, Measurements, Recurring [Member] | Level 2 | State and municipal
Fair value measurements
Trading account assets		8		3
Fair Value, Measurements, Recurring [Member] | Level 2 | Commercial Paper
Fair value measurements
Trading account assets				25
Fair Value, Measurements, Recurring [Member] | Level 2 | Interest rate derivative contracts
Fair value measurements
Trading account assets		1,394		998
Trading account liabilities		1,344		947
Fair Value, Measurements, Recurring [Member] | Level 2 | Commodity derivative contracts
Fair value measurements
Trading account assets		367		408
Trading account liabilities		330		368
Fair Value, Measurements, Recurring [Member] | Level 2 | Foreign exchange derivative contracts
Fair value measurements
Trading account assets		111		115
Trading account liabilities		130		91
Fair Value, Measurements, Recurring [Member] | Level 2 | Residential mortgage-backed securities, U.S. government agency and government-sponsored agencies
Fair value measurements
Securities available for sale		6,308		7,201
Fair Value, Measurements, Recurring [Member] | Level 2 | Residential mortgage-backed securities, Privately issued
Fair value measurements
Securities available for sale		203		151
Fair Value, Measurements, Recurring [Member] | Level 2 | Privately issued commercial mortgage-backed securities
Fair value measurements
Securities available for sale		1,492		1,546
Fair Value, Measurements, Recurring [Member] | Level 2 | Collateralized loan obligations
Fair value measurements
Securities available for sale		3,227		3,233
Fair Value, Measurements, Recurring [Member] | Level 2 | Other Asset Liability Management Securities
Fair value measurements
Securities available for sale		7		7
Fair Value, Measurements, Recurring [Member] | Level 2 | Other debt securities, Other
Fair value measurements
Securities available for sale		1		1
Fair Value, Measurements, Recurring [Member] | Level 2 | Interest rate hedging contracts
Fair value measurements
Other assets		271		73
Other liabilities				14
Fair Value, Measurements, Recurring [Member] | Level 2 | Other derivative contracts
Fair value measurements
Other assets		3		4
Other liabilities		1		0
Fair Value, Measurements, Recurring [Member] | Level 2 | Securities sold, not yet purchased
Fair value measurements
Trading account liabilities		19		23
Fair Value, Measurements, Recurring [Member] | Level 3
Fair value measurements
Trading account assets		189		228
Securities available for sale		1,613		1,603
Other assets		15		1
Total assets		$ 1,817		$ 1,832
Percentage of Total		13.00%		12.00%
Percentage of Total Company Assets		2.00%		2.00%
Trading account liabilities		$ 187		$ 223
FDIC clawback liability				112
Other liabilities		116		114
Total liabilities		$ 303		$ 337
Percentage of Total		35.00%		37.00%
Percentage of Total Company Liabilities		0.00%		0.00%
Fair Value, Measurements, Recurring [Member] | Level 3 | Interest rate derivative contracts
Fair value measurements
Trading account assets		$ 2		$ 4
Fair Value, Measurements, Recurring [Member] | Level 3 | Commodity derivative contracts
Fair value measurements
Trading account assets		3		1
Trading account liabilities		3		1
Fair Value, Measurements, Recurring [Member] | Level 3 | Foreign exchange derivative contracts
Fair value measurements
Trading account assets		1		1
Trading account liabilities		1		1
Fair Value, Measurements, Recurring [Member] | Level 3 | Equity Derivative contracts
Fair value measurements
Trading account assets		183		222
Trading account liabilities		183		221
Fair Value, Measurements, Recurring [Member] | Level 3 | Other debt securities, Direct bank purchase bonds
Fair value measurements
Securities available for sale		1,581		1,572
Fair Value, Measurements, Recurring [Member] | Level 3 | Other debt securities, Other
Fair value measurements
Securities available for sale		32		31
Fair Value, Measurements, Recurring [Member] | Level 3 | Mortgage servicing rights [Domain]
Fair value measurements
Other assets		13
Fair Value, Measurements, Recurring [Member] | Level 3 | Other derivative contracts
Fair value measurements
Other assets		2		1
Other liabilities		$ 1		$ 2
Fair Value, Measurements, Recurring [Member] | Netting [Member]
Fair value measurements
Percentage of Total		(7.00%)	[1]	(6.00%)	[2]
Percentage of Total Company Assets		(1.00%)	[1]	(1.00%)	[2]
Percentage of Total		(146.00%)	[1]	(96.00%)	[2]
Percentage of Total Company Liabilities		(1.00%)	[1]	(1.00%)	[2]
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Interest rate derivative contracts
Fair value measurements
Trading account assets		$ (254)	[1]	$ (163)	[2]
Trading account liabilities		(1,150)	[1]	(775)	[2]
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Commodity derivative contracts
Fair value measurements
Trading account assets		(351)	[1]	(384)	[2]
Trading account liabilities		(78)	[1]	(61)	[2]
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Foreign exchange derivative contracts
Fair value measurements
Trading account assets		(54)	[1]	(70)	[2]
Trading account liabilities		(38)	[1]	(22)	[2]
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Equity Derivative contracts
Fair value measurements
Trading account assets		(175)	[1]	(217)	[2]
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Interest rate hedging contracts
Fair value measurements
Other assets		(205)	[1]	(71)	[2]
Trading account liabilities	[2]			(14)
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Other derivative contracts
Fair value measurements
Other assets		(3)	[1]	(4)	[2]
Fair Value
Fair value measurements
Other assets				17
Fair Value | Fair Value, Measurements, Recurring [Member]
Fair value measurements
Trading account assets		1,370		1,087
Securities available for sale		13,011		14,344
Other assets		81		3
Total assets		14,462		$ 15,434
Percentage of Total				100.00%
Percentage of Total Company Assets				13.00%
Trading account liabilities		747		$ 796
FDIC clawback liability		115		112
Other liabilities		117		114
Total liabilities		864		$ 910
Percentage of Total				100.00%
Percentage of Total Company Liabilities				0.00%
Fair Value | Fair Value, Measurements, Recurring [Member] | U.S. Treasury
Fair value measurements
Trading account assets		36		$ 37
Securities available for sale		152		594
Fair Value | Fair Value, Measurements, Recurring [Member] | U.S. government-sponsored agencies
Fair value measurements
Trading account assets		97		106
Fair Value | Fair Value, Measurements, Recurring [Member] | State and municipal
Fair value measurements
Trading account assets		8		3
Fair Value | Fair Value, Measurements, Recurring [Member] | Commercial Paper
Fair value measurements
Trading account assets				25
Fair Value | Fair Value, Measurements, Recurring [Member] | Interest rate derivative contracts
Fair value measurements
Trading account assets		1,143		839
Trading account liabilities		197		173
Fair Value | Fair Value, Measurements, Recurring [Member] | Commodity derivative contracts
Fair value measurements
Trading account assets		19		25
Trading account liabilities		255		308
Fair Value | Fair Value, Measurements, Recurring [Member] | Foreign exchange derivative contracts
Fair value measurements
Trading account assets		59		47
Trading account liabilities		93		71
Fair Value | Fair Value, Measurements, Recurring [Member] | Equity Derivative contracts
Fair value measurements
Trading account assets		8		5
Trading account liabilities		183		221
Fair Value | Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed securities, U.S. government agency and government-sponsored agencies
Fair value measurements
Securities available for sale		6,308		7,201
Fair Value | Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed securities, Privately issued
Fair value measurements
Securities available for sale		203		151
Fair Value | Fair Value, Measurements, Recurring [Member] | Privately issued commercial mortgage-backed securities
Fair value measurements
Securities available for sale		1,492		1,546
Fair Value | Fair Value, Measurements, Recurring [Member] | Collateralized loan obligations
Fair value measurements
Securities available for sale		3,227		3,233
Fair Value | Fair Value, Measurements, Recurring [Member] | Other Asset Liability Management Securities
Fair value measurements
Securities available for sale		7		7
Fair Value | Fair Value, Measurements, Recurring [Member] | Other debt securities, Direct bank purchase bonds
Fair value measurements
Securities available for sale		1,581		1,572
Fair Value | Fair Value, Measurements, Recurring [Member] | Other debt securities, Other
Fair value measurements
Securities available for sale		33		32
Fair Value | Fair Value, Measurements, Recurring [Member] | Equity securities
Fair value measurements
Securities available for sale		8		8
Fair Value | Fair Value, Measurements, Recurring [Member] | Mortgage servicing rights [Domain]
Fair value measurements
Other assets		13
Fair Value | Fair Value, Measurements, Recurring [Member] | Interest rate hedging contracts
Fair value measurements
Other assets		66		2
Other liabilities				0
Fair Value | Fair Value, Measurements, Recurring [Member] | Other derivative contracts
Fair value measurements
Other assets		2		1
Other liabilities		2		2
Fair Value | Fair Value, Measurements, Recurring [Member] | Securities sold, not yet purchased
Fair value measurements
Trading account liabilities		19		$ 23
Fdic | Fair Value, Measurements, Recurring [Member] | Level 3
Fair value measurements
FDIC clawback liability		$ 115

[1] Amounts represent the impact of legally enforceable master netting agreements between the same counterparties that allow the Company to net settle all contracts.

[2] Amounts represent the impact of legally enforceable master netting agreements between the same counterparties that allow the Company to net settle all contracts.