Derivatives, Fair Value of Derivatives Contracts (Details) - USD ($) $ in Thousands		Sep. 30, 2016		Dec. 31, 2015		Sep. 30, 2015
Derivative Assets, Fair Value, Net [Abstract]
Derviative contracts, net of cash collateral, Assets, Fair value		$ 655,078		$ 586,270		$ 726,159
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Net of Cash Collateral		573,987		581,701		636,115
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]	25,136,553		17,153,221		18,911,244
Derivative Liabilities, Notional		23,988,858	[2]	16,785,014	[1]	18,819,086	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		734,256		663,343		838,694
Derivative Assets, Netting Adjustments		(68,713)		(52,433)		(83,433)
Derivative Assets, Net Fair Value Before Cash Collateral		665,543		610,910		755,261
Derivative Assets, Cash Collateral		(10,465)		(24,640)		(29,102)
Derviative contracts, net of cash collateral, Assets, Fair value		655,078		586,270		726,159
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		725,452		659,171		831,115
Derivative Liabilities, Netting Adjustments		(68,713)		(52,433)		(83,433)
Derivative Liabilities, Net Fair Value Before Cash Collateral		656,739		606,738		747,682
Derivative Liabilities, Cash Collateral		(82,752)		(25,037)		(111,567)
Derivative Liabilities, Fair Value, Net of Cash Collateral		573,987		581,701		636,115
Not Designated as Hedging Instrument [Member] | To-be-announced residential mortgage-backed securities
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	20,078,974		14,583,052		16,093,704
Derivative Liabilities, Notional		19,776,883	[2]	14,168,927	[3]	16,050,271	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		90,999		43,270		136,435
Derivative Assets, Netting Adjustments		(38,678)		(28,305)		(50,845)
Derivative Assets, Net Fair Value Before Cash Collateral		52,321		14,965		85,590
Derivative Assets, Cash Collateral		0		0		0
Derviative contracts, net of cash collateral, Assets, Fair value		52,321		14,965		85,590
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		86,812		40,141		133,543
Derivative Liabilities, Netting Adjustments		(38,678)		(28,305)		(50,845)
Derivative Liabilities, Net Fair Value Before Cash Collateral		48,134		11,836		82,698
Derivative Liabilities, Cash Collateral		(39,042)		(1,308)		(82,225)
Derivative Liabilities, Fair Value, Net of Cash Collateral		9,092		10,528		473
Not Designated as Hedging Instrument [Member] | Interest rate swaps
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[3]	1,323,045		1,332,044		1,345,779
Derivative Liabilities, Notional		1,323,045	[2]	1,332,044	[3]	1,345,779	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		49,279		31,744		42,636
Derivative Assets, Netting Adjustments		0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral		49,279		31,744		42,636
Derivative Assets, Cash Collateral		(794)		(1,424)		0
Derviative contracts, net of cash collateral, Assets, Fair value		48,485		30,320		42,636
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		49,518		31,928		42,901
Derivative Liabilities, Netting Adjustments		0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral		49,518		31,928		42,901
Derivative Liabilities, Cash Collateral		(34,457)		(20,530)		(26,723)
Derivative Liabilities, Fair Value, Net of Cash Collateral		15,061		11,398		16,178
Not Designated as Hedging Instrument [Member] | Energy contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	729,202		470,613		560,997
Derivative Liabilities, Notional		695,835	[2]	463,703	[3]	551,989	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		41,775		83,045		89,948
Derivative Assets, Netting Adjustments		(28,464)		(22,970)		(28,535)
Derivative Assets, Net Fair Value Before Cash Collateral		13,311		60,075		61,413
Derivative Assets, Cash Collateral		(288)		(18,606)		(23,089)
Derviative contracts, net of cash collateral, Assets, Fair value		13,023		41,469		38,324
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		40,888		81,869		85,856
Derivative Liabilities, Netting Adjustments		(28,464)		(22,970)		(28,535)
Derivative Liabilities, Net Fair Value Before Cash Collateral		12,424		58,899		57,321
Derivative Liabilities, Cash Collateral		(3,857)		0		0
Derivative Liabilities, Fair Value, Net of Cash Collateral		8,567		58,899		57,321
Not Designated as Hedging Instrument [Member] | Agricultural contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	53,002		61,662		101,321
Derivative Liabilities, Notional		52,997	[2]	61,657	[3]	101,325	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		3,950		2,591		8,064
Derivative Assets, Netting Adjustments		(1,571)		(1,158)		(4,053)
Derivative Assets, Net Fair Value Before Cash Collateral		2,379		1,433		4,011
Derivative Assets, Cash Collateral		(1,076)		0		(1,558)
Derviative contracts, net of cash collateral, Assets, Fair value		1,303		1,433		2,453
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		3,943		2,579		8,045
Derivative Liabilities, Netting Adjustments		(1,571)		(1,158)		(4,053)
Derivative Liabilities, Net Fair Value Before Cash Collateral		2,372		1,421		3,992
Derivative Liabilities, Cash Collateral		0		(1,248)		0
Derivative Liabilities, Fair Value, Net of Cash Collateral		2,372		173		3,992
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	550,828		546,572		618,991
Derivative Liabilities, Notional		550,943	[2]	546,405	[3]	618,770	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		536,264		498,830		557,313
Derivative Assets, Netting Adjustments		0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral		536,264		498,830		557,313
Derivative Assets, Cash Collateral		(7,577)		(4,140)		(3,985)
Derviative contracts, net of cash collateral, Assets, Fair value		528,687		494,690		553,328
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		536,660		498,574		556,890
Derivative Liabilities, Netting Adjustments		0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral		536,660		498,574		556,890
Derivative Liabilities, Cash Collateral		(5,396)		(1,951)		(2,619)
Derivative Liabilities, Fair Value, Net of Cash Collateral		531,264		496,623		554,271
Not Designated as Hedging Instrument [Member] | Equity option contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	103,464		137,278		143,452
Derivative Liabilities, Notional		103,464	[2]	137,278	[3]	143,452	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		4,654		3,780		3,784
Derivative Assets, Netting Adjustments		0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral		4,654		3,780		3,784
Derivative Assets, Cash Collateral		(730)		(470)		(470)
Derviative contracts, net of cash collateral, Assets, Fair value		3,924		3,310		3,314
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		4,654		3,780		3,784
Derivative Liabilities, Netting Adjustments		0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral		4,654		3,780		3,784
Derivative Liabilities, Cash Collateral		0		0		0
Derivative Liabilities, Fair Value, Net of Cash Collateral		4,654		3,780		3,784
Not Designated as Hedging Instrument [Member] | Total customer risk management programs
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	22,838,515		17,131,221		18,864,244
Derivative Liabilities, Notional		22,503,167	[2]	16,710,014	[3]	18,811,586	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		726,921		663,260		838,180
Derivative Assets, Netting Adjustments		(68,713)		(52,433)		(83,433)
Derivative Assets, Net Fair Value Before Cash Collateral		658,208		610,827		754,747
Derivative Assets, Cash Collateral		(10,465)		(24,640)		(29,102)
Derviative contracts, net of cash collateral, Assets, Fair value		647,743		586,187		725,645
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		722,475		658,871		831,019
Derivative Liabilities, Netting Adjustments		(68,713)		(52,433)		(83,433)
Derivative Liabilities, Net Fair Value Before Cash Collateral		653,762		606,438		747,586
Derivative Liabilities, Cash Collateral		(82,752)		(25,037)		(111,567)
Derivative Liabilities, Fair Value, Net of Cash Collateral		571,010		581,401		636,019
Not Designated as Hedging Instrument [Member] | Internal risk management programs
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	[1]	2,298,038		22,000		47,000
Derivative Liabilities, Notional		1,485,691	[2]	75,000	[3]	7,500	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value		7,335		83		514
Derivative Assets, Netting Adjustments		0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral		7,335		83		514
Derivative Assets, Cash Collateral		0		0		0
Derviative contracts, net of cash collateral, Assets, Fair value		7,335		83		514
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value		2,977		300		96
Derivative Liabilities, Netting Adjustments		0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral		2,977		300		96
Derivative Liabilities, Cash Collateral		0		0		0
Derivative Liabilities, Fair Value, Net of Cash Collateral		$ 2,977		$ 300		$ 96

[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.