Derivatives, Fair Value of Derivatives Contracts (Details) - USD ($) $ in Thousands	Sep. 30, 2017		Dec. 31, 2016		Sep. 30, 2016
Derivative Assets, Fair Value, Net [Abstract]
Derviative contracts, net of cash collateral, Assets, Fair value	$ 352,559		$ 689,872		$ 655,078
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Net of Cash Collateral	336,327		664,531		573,987
Not Designated as Hedging Instrument [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	28,952,817	[1]	22,437,314	[2]	25,136,553	[3]
Derivative Liabilities, Notional	26,144,409	[1]	22,178,359	[2]	23,988,858	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	402,422		789,791		734,256
Derivative Assets, Netting Adjustments	(45,885)		(89,368)		(68,713)
Derivative Assets, Net Fair Value Before Cash Collateral	356,537		700,423		665,543
Derivative Assets, Cash Collateral	(3,978)		(10,551)		(10,465)
Derviative contracts, net of cash collateral, Assets, Fair value	352,559		689,872		655,078
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	400,580		801,809		725,452
Derivative Liabilities, Netting Adjustments	(45,885)		(89,368)		(68,713)
Derivative Liabilities, Net Fair Value Before Cash Collateral	354,695		712,441		656,739
Derivative Liabilities, Cash Collateral	(18,368)		(47,910)		(82,752)
Derivative Liabilities, Fair Value, Net of Cash Collateral	336,327		664,531		573,987
Not Designated as Hedging Instrument [Member] | To-be-announced residential mortgage-backed securities
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	14,244,442	[1]	16,949,152	[2]	20,078,974	[3]
Derivative Liabilities, Notional	14,244,442	[1]	16,637,532	[2]	19,776,883	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	38,875		180,695		90,999
Derivative Assets, Netting Adjustments	(9,547)		(60,555)		(38,678)
Derivative Assets, Net Fair Value Before Cash Collateral	29,328		120,140		52,321
Derivative Assets, Cash Collateral	0		0		0
Derviative contracts, net of cash collateral, Assets, Fair value	29,328		120,140		52,321
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	34,948		176,928		86,812
Derivative Liabilities, Netting Adjustments	(9,547)		(60,555)		(38,678)
Derivative Liabilities, Net Fair Value Before Cash Collateral	25,401		116,373		48,134
Derivative Liabilities, Cash Collateral	(374)		0		(39,042)
Derivative Liabilities, Fair Value, Net of Cash Collateral	25,027		116,373		9,092
Not Designated as Hedging Instrument [Member] | Interest rate swaps
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	1,368,210	[1]	1,403,408	[2]	1,323,045	[3]
Derivative Liabilities, Notional	1,368,230	[1]	1,403,408	[2]	1,323,045	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	27,016		34,442		49,279
Derivative Assets, Netting Adjustments	0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral	27,016		34,442		49,279
Derivative Assets, Cash Collateral	(2,820)		(4,567)		(794)
Derviative contracts, net of cash collateral, Assets, Fair value	24,196		29,875		48,485
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	27,056		34,442		49,518
Derivative Liabilities, Netting Adjustments	0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	27,056		34,442		49,518
Derivative Liabilities, Cash Collateral	(16,599)		(11,977)		(34,457)
Derivative Liabilities, Fair Value, Net of Cash Collateral	10,457		22,465		15,061
Not Designated as Hedging Instrument [Member] | Energy contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	983,794	[1]	835,566	[2]	729,202	[3]
Derivative Liabilities, Notional	939,350	[1]	820,365	[2]	695,835	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	45,368		64,140		41,775
Derivative Assets, Netting Adjustments	(35,166)		(28,298)		(28,464)
Derivative Assets, Net Fair Value Before Cash Collateral	10,202		35,842		13,311
Derivative Assets, Cash Collateral	(238)		(71)		(288)
Derviative contracts, net of cash collateral, Assets, Fair value	9,964		35,771		13,023
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	42,744		64,306		40,888
Derivative Liabilities, Netting Adjustments	(35,166)		(28,298)		(28,464)
Derivative Liabilities, Net Fair Value Before Cash Collateral	7,578		36,008		12,424
Derivative Liabilities, Cash Collateral	0		(31,534)		(3,857)
Derivative Liabilities, Fair Value, Net of Cash Collateral	7,578		4,474		8,567
Not Designated as Hedging Instrument [Member] | Agricultural contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	60,745	[1]	53,209	[2]	53,002	[3]
Derivative Liabilities, Notional	60,746	[1]	53,216	[2]	52,997	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	1,870		1,382		3,950
Derivative Assets, Netting Adjustments	(1,172)		(515)		(1,571)
Derivative Assets, Net Fair Value Before Cash Collateral	698		867		2,379
Derivative Assets, Cash Collateral	0		0		(1,076)
Derviative contracts, net of cash collateral, Assets, Fair value	698		867		1,303
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	1,846		1,365		3,943
Derivative Liabilities, Netting Adjustments	(1,172)		(515)		(1,571)
Derivative Liabilities, Net Fair Value Before Cash Collateral	674		850		2,372
Derivative Liabilities, Cash Collateral	0		(769)		0
Derivative Liabilities, Fair Value, Net of Cash Collateral	674		81		2,372
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	252,525	[1]	580,886	[2]	550,828	[3]
Derivative Liabilities, Notional	249,269	[1]	580,712	[2]	550,943	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	249,788		494,349		536,264
Derivative Assets, Netting Adjustments	0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral	249,788		494,349		536,264
Derivative Assets, Cash Collateral	0		(5,183)		(7,577)
Derviative contracts, net of cash collateral, Assets, Fair value	249,788		489,166		528,687
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	245,925		494,695		536,660
Derivative Liabilities, Netting Adjustments	0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	245,925		494,695		536,660
Derivative Liabilities, Cash Collateral	(1,395)		(3,630)		(5,396)
Derivative Liabilities, Fair Value, Net of Cash Collateral	244,530		491,065		531,264
Not Designated as Hedging Instrument [Member] | Equity option contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	101,841	[1]	100,924	[2]	103,464	[3]
Derivative Liabilities, Notional	101,841	[1]	100,924	[2]	103,464	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	4,871		4,357		4,654
Derivative Assets, Netting Adjustments	0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral	4,871		4,357		4,654
Derivative Assets, Cash Collateral	(920)		(730)		(730)
Derviative contracts, net of cash collateral, Assets, Fair value	3,951		3,627		3,924
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	4,871		4,357		4,654
Derivative Liabilities, Netting Adjustments	0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	4,871		4,357		4,654
Derivative Liabilities, Cash Collateral	0		0		0
Derivative Liabilities, Fair Value, Net of Cash Collateral	4,871		4,357		4,654
Not Designated as Hedging Instrument [Member] | Total customer risk management programs
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	17,011,557	[1]	19,923,145	[2]	22,838,515	[3]
Derivative Liabilities, Notional	16,963,878	[1]	19,596,157	[2]	22,503,167	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	367,788		779,365		726,921
Derivative Assets, Netting Adjustments	(45,885)		(89,368)		(68,713)
Derivative Assets, Net Fair Value Before Cash Collateral	321,903		689,997		658,208
Derivative Assets, Cash Collateral	(3,978)		(10,551)		(10,465)
Derviative contracts, net of cash collateral, Assets, Fair value	317,925		679,446		647,743
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	357,390		776,093		722,475
Derivative Liabilities, Netting Adjustments	(45,885)		(89,368)		(68,713)
Derivative Liabilities, Net Fair Value Before Cash Collateral	311,505		686,725		653,762
Derivative Liabilities, Cash Collateral	(18,368)		(47,910)		(82,752)
Derivative Liabilities, Fair Value, Net of Cash Collateral	293,137		638,815		571,010
Not Designated as Hedging Instrument [Member] | Internal risk management programs
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	11,941,260	[1]	2,514,169	[2]	2,298,038	[3]
Derivative Liabilities, Notional	9,180,531	[1]	2,582,202	[2]	1,485,691	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	34,634		10,426		7,335
Derivative Assets, Netting Adjustments	0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral	34,634		10,426		7,335
Derivative Assets, Cash Collateral	0		0		0
Derviative contracts, net of cash collateral, Assets, Fair value	34,634		10,426		7,335
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	43,190		25,716		2,977
Derivative Liabilities, Netting Adjustments	0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	43,190		25,716		2,977
Derivative Liabilities, Cash Collateral	0		0		0
Derivative Liabilities, Fair Value, Net of Cash Collateral	$ 43,190		$ 25,716		$ 2,977

[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.