Derivatives, Fair Value of Derivatives Contracts (Details) - USD ($) $ in Thousands		Jun. 30, 2016		Dec. 31, 2015		Jun. 30, 2015
Derivative Assets, Fair Value, Net [Abstract]
Derviative contracts, net of cash collateral, Assets, Fair value		$ 883,673		$ 586,270		$ 630,435
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Net of Cash Collateral		719,159		581,701		620,277
Increase in cash margin obligation for derivative holdings with a decrease in credit rating from A1 to below investment grade		18,000
Not Designated as Hedging Instrument [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	23,037,973		17,153,221		20,215,152
Derivative Liabilities, Notional		21,565,820	[2]	16,785,014	[1]	20,682,559	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		993,485		663,343		736,632
Derivative Assets, Netting Adjustments		(102,988)		(52,433)		(84,842)
Derivative Assets, Net Fair Value Before Cash Collateral		890,497		610,910		651,790
Derivative Assets, Cash Collateral		(6,824)		(24,640)		(21,355)
Derviative contracts, net of cash collateral, Assets, Fair value		883,673		586,270		630,435
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		974,975		659,171		728,309
Derivative Liabilities, Netting Adjustments		(102,988)		(52,433)		(84,842)
Derivative Liabilities, Net Fair Value Before Cash Collateral		871,987		606,738		643,467
Derivative Liabilities, Cash Collateral		(152,828)		(25,037)		(23,190)
Derivative Liabilities, Fair Value, Net of Cash Collateral		719,159		581,701		620,277
Not Designated as Hedging Instrument [Member] | To-be-announced residential mortgage-backed securities [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	18,774,134		14,583,052		17,412,925
Derivative Liabilities, Notional		18,662,334	[2]	14,168,927	[3]	17,863,884	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		183,118		43,270		116,138
Derivative Assets, Netting Adjustments		(67,383)		(28,305)		(42,003)
Derivative Assets, Net Fair Value Before Cash Collateral		115,735		14,965		74,135
Derivative Assets, Cash Collateral		0		0		0
Derviative contracts, net of cash collateral, Assets, Fair value		115,735		14,965		74,135
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		179,443		40,141		112,166
Derivative Liabilities, Netting Adjustments		(67,383)		(28,305)		(42,003)
Derivative Liabilities, Net Fair Value Before Cash Collateral		112,060		11,836		70,163
Derivative Liabilities, Cash Collateral		(103,724)		(1,308)		0
Derivative Liabilities, Fair Value, Net of Cash Collateral		8,336		10,528		70,163
Not Designated as Hedging Instrument [Member] | Interest rate swaps [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[3]	1,299,985		1,332,044		1,282,503
Derivative Liabilities, Notional		1,299,985	[2]	1,332,044	[3]	1,282,503	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		54,978		31,744		33,311
Derivative Assets, Netting Adjustments		0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral		54,978		31,744		33,311
Derivative Assets, Cash Collateral		(1,100)		(1,424)		(70)
Derviative contracts, net of cash collateral, Assets, Fair value		53,878		30,320		33,241
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		55,404		31,928		33,471
Derivative Liabilities, Netting Adjustments		0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral		55,404		31,928		33,471
Derivative Liabilities, Cash Collateral		(32,597)		(20,530)		(17,889)
Derivative Liabilities, Fair Value, Net of Cash Collateral		22,807		11,398		15,582
Not Designated as Hedging Instrument [Member] | Energy contracts [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	757,669		470,613		711,123
Derivative Liabilities, Notional		734,538	[2]	463,703	[3]	676,214	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		59,103		83,045		82,871
Derivative Assets, Netting Adjustments		(33,996)		(22,970)		(42,115)
Derivative Assets, Net Fair Value Before Cash Collateral		25,107		60,075		40,756
Derivative Assets, Cash Collateral		(155)		(18,606)		(20,122)
Derviative contracts, net of cash collateral, Assets, Fair value		24,952		41,469		20,634
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		58,033		81,869		78,044
Derivative Liabilities, Netting Adjustments		(33,996)		(22,970)		(42,115)
Derivative Liabilities, Net Fair Value Before Cash Collateral		24,037		58,899		35,929
Derivative Liabilities, Cash Collateral		(11,784)		0		0
Derivative Liabilities, Fair Value, Net of Cash Collateral		12,253		58,899		35,929
Not Designated as Hedging Instrument [Member] | Agricultural contracts [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	50,848		61,662		66,430
Derivative Liabilities, Notional		50,843	[2]	61,657	[3]	66,433	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		2,488		2,591		1,367
Derivative Assets, Netting Adjustments		(1,609)		(1,158)		(724)
Derivative Assets, Net Fair Value Before Cash Collateral		879		1,433		643
Derivative Assets, Cash Collateral		(37)		0		0
Derviative contracts, net of cash collateral, Assets, Fair value		842		1,433		643
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		2,476		2,579		1,355
Derivative Liabilities, Netting Adjustments		(1,609)		(1,158)		(724)
Derivative Liabilities, Net Fair Value Before Cash Collateral		867		1,421		631
Derivative Liabilities, Cash Collateral		0		(1,248)		(475)
Derivative Liabilities, Fair Value, Net of Cash Collateral		867		173		156
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	701,436		546,572		574,049
Derivative Liabilities, Notional		701,219	[2]	546,405	[3]	573,403	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		675,804		498,830		495,952
Derivative Assets, Netting Adjustments		0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral		675,804		498,830		495,952
Derivative Assets, Cash Collateral		(5,054)		(4,140)		(1,100)
Derviative contracts, net of cash collateral, Assets, Fair value		670,750		494,690		494,852
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		675,383		498,574		495,320
Derivative Liabilities, Netting Adjustments		0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral		675,383		498,574		495,320
Derivative Liabilities, Cash Collateral		(4,723)		(1,951)		(4,826)
Derivative Liabilities, Fair Value, Net of Cash Collateral		670,660		496,623		490,494
Not Designated as Hedging Instrument [Member] | Equity option contracts [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	116,901		137,278		168,122
Derivative Liabilities, Notional		116,901	[2]	137,278	[3]	168,122	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		4,236		3,780		6,993
Derivative Assets, Netting Adjustments		0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral		4,236		3,780		6,993
Derivative Assets, Cash Collateral		(478)		(470)		(63)
Derviative contracts, net of cash collateral, Assets, Fair value		3,758		3,310		6,930
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		4,236		3,780		6,993
Derivative Liabilities, Netting Adjustments		0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral		4,236		3,780		6,993
Derivative Liabilities, Cash Collateral		0		0		0
Derivative Liabilities, Fair Value, Net of Cash Collateral		4,236		3,780		6,993
Not Designated as Hedging Instrument [Member] | Total customer risk management programs [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	21,700,973		17,131,221		20,215,152
Derivative Liabilities, Notional		21,565,820	[2]	16,710,014	[3]	20,630,559	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		979,727		663,260		736,632
Derivative Assets, Netting Adjustments		(102,988)		(52,433)		(84,842)
Derivative Assets, Net Fair Value Before Cash Collateral		876,739		610,827		651,790
Derivative Assets, Cash Collateral		(6,824)		(24,640)		(21,355)
Derviative contracts, net of cash collateral, Assets, Fair value		869,915		586,187		630,435
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		974,975		658,871		727,349
Derivative Liabilities, Netting Adjustments		(102,988)		(52,433)		(84,842)
Derivative Liabilities, Net Fair Value Before Cash Collateral		871,987		606,438		642,507
Derivative Liabilities, Cash Collateral		(152,828)		(25,037)		(23,190)
Derivative Liabilities, Fair Value, Net of Cash Collateral		719,159		581,401		619,317
Not Designated as Hedging Instrument [Member] | Interest rate risk management programs [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	1,337,000		22,000		0
Derivative Liabilities, Notional		0	[2]	75,000	[3]	52,000	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		13,758		83		0
Derivative Assets, Netting Adjustments		0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral		13,758		83		0
Derivative Assets, Cash Collateral		0		0		0
Derviative contracts, net of cash collateral, Assets, Fair value		13,758		83		0
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		0		300		960
Derivative Liabilities, Netting Adjustments		0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral		0		300		960
Derivative Liabilities, Cash Collateral		0		0		0
Derivative Liabilities, Fair Value, Net of Cash Collateral		$ 0		$ 300		$ 960

[1] Notional amounts for commodity contracts are converted into dollar-equivalent amounts based on dollar prices at the inception of the contract.

[2] Notional amounts for commodity contracts are converted into dollar-equivalent amounts based on dollar prices at the inception of the contract.

[3] Notional amounts for commodity contracts are converted into dollar-equivalent amounts based on dollar prices at the inception of the contract.