Derivatives, Fair Value of Derivatives Contracts (Details) - USD ($) $ in Thousands	Mar. 31, 2017		Dec. 31, 2016		Mar. 31, 2016
Derivative Assets, Fair Value, Net [Abstract]
Derviative contracts, net of cash collateral, Assets, Fair value	$ 304,727		$ 689,872		$ 790,146
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Net of Cash Collateral	276,422		664,531		705,578
Increase in cash margin obligation for derivative holdings with a decrease in credit rating from A1 to below investment grade	10,000
Not Designated as Hedging Instrument [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	20,047,451	[1]	22,437,314	[2]	19,792,138	[3]
Derivative Liabilities, Notional	18,107,686	[1]	22,178,359	[2]	19,101,068	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	371,995		789,791		873,951
Derivative Assets, Netting Adjustments	(62,384)		(89,368)		(67,119)
Derivative Assets, Net Fair Value Before Cash Collateral	309,611		700,423		806,832
Derivative Assets, Cash Collateral	(4,884)		(10,551)		(16,686)
Derviative contracts, net of cash collateral, Assets, Fair value	304,727		689,872		790,146
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	378,140		801,809		863,433
Derivative Liabilities, Netting Adjustments	(62,384)		(89,368)		(67,119)
Derivative Liabilities, Net Fair Value Before Cash Collateral	315,756		712,441		796,314
Derivative Liabilities, Cash Collateral	(39,334)		(47,910)		(90,736)
Derivative Liabilities, Fair Value, Net of Cash Collateral	276,422		664,531		705,578
Not Designated as Hedging Instrument [Member] | To-be-announced residential mortgage-backed securities
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	14,549,828	[1]	16,949,152	[2]	16,235,517	[3]
Derivative Liabilities, Notional	14,322,223	[1]	16,637,532	[2]	16,323,807	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	80,272		180,695		111,188
Derivative Assets, Netting Adjustments	(33,143)		(60,555)		(44,570)
Derivative Assets, Net Fair Value Before Cash Collateral	47,129		120,140		66,618
Derivative Assets, Cash Collateral	0		0		0
Derviative contracts, net of cash collateral, Assets, Fair value	47,129		120,140		66,618
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	76,971		176,928		107,541
Derivative Liabilities, Netting Adjustments	(33,143)		(60,555)		(44,570)
Derivative Liabilities, Net Fair Value Before Cash Collateral	43,828		116,373		62,971
Derivative Liabilities, Cash Collateral	(34,310)		0		(61,380)
Derivative Liabilities, Fair Value, Net of Cash Collateral	9,518		116,373		1,591
Not Designated as Hedging Instrument [Member] | Interest rate swaps
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	1,491,414	[1]	1,403,408	[2]	1,335,259	[3]
Derivative Liabilities, Notional	1,491,414	[1]	1,403,408	[2]	1,335,259	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	32,286		34,442		48,270
Derivative Assets, Netting Adjustments	0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral	32,286		34,442		48,270
Derivative Assets, Cash Collateral	(3,349)		(4,567)		0
Derviative contracts, net of cash collateral, Assets, Fair value	28,937		29,875		48,270
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	33,036		34,442		48,619
Derivative Liabilities, Netting Adjustments	0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	33,036		34,442		48,619
Derivative Liabilities, Cash Collateral	0		(11,977)		(28,572)
Derivative Liabilities, Fair Value, Net of Cash Collateral	33,036		22,465		20,047
Not Designated as Hedging Instrument [Member] | Energy contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	886,699	[1]	835,566	[2]	533,355	[3]
Derivative Liabilities, Notional	844,406	[1]	820,365	[2]	526,103	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	42,598		64,140		62,365
Derivative Assets, Netting Adjustments	(28,455)		(28,298)		(21,374)
Derivative Assets, Net Fair Value Before Cash Collateral	14,143		35,842		40,991
Derivative Assets, Cash Collateral	(543)		(71)		(11,340)
Derviative contracts, net of cash collateral, Assets, Fair value	13,600		35,771		29,651
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	40,604		64,306		62,528
Derivative Liabilities, Netting Adjustments	(28,455)		(28,298)		(21,374)
Derivative Liabilities, Net Fair Value Before Cash Collateral	12,149		36,008		41,154
Derivative Liabilities, Cash Collateral	(258)		(31,534)		0
Derivative Liabilities, Fair Value, Net of Cash Collateral	11,891		4,474		41,154
Not Designated as Hedging Instrument [Member] | Agricultural contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	51,679	[1]	53,209	[2]	104,927	[3]
Derivative Liabilities, Notional	51,509	[1]	53,216	[2]	104,922	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	2,031		1,382		1,859
Derivative Assets, Netting Adjustments	(786)		(515)		(1,175)
Derivative Assets, Net Fair Value Before Cash Collateral	1,245		867		684
Derivative Assets, Cash Collateral	0		0		0
Derviative contracts, net of cash collateral, Assets, Fair value	1,245		867		684
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	2,015		1,365		1,847
Derivative Liabilities, Netting Adjustments	(786)		(515)		(1,175)
Derivative Liabilities, Net Fair Value Before Cash Collateral	1,229		850		672
Derivative Liabilities, Cash Collateral	(1,040)		(769)		(420)
Derivative Liabilities, Fair Value, Net of Cash Collateral	189		81		252
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	211,837	[1]	580,886	[2]	682,457	[3]
Derivative Liabilities, Notional	208,236	[1]	580,712	[2]	682,354	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	204,774		494,349		639,322
Derivative Assets, Netting Adjustments	0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral	204,774		494,349		639,322
Derivative Assets, Cash Collateral	(72)		(5,183)		(4,970)
Derviative contracts, net of cash collateral, Assets, Fair value	204,702		489,166		634,352
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	201,043		494,695		638,892
Derivative Liabilities, Netting Adjustments	0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	201,043		494,695		638,892
Derivative Liabilities, Cash Collateral	(3,726)		(3,630)		(364)
Derivative Liabilities, Fair Value, Net of Cash Collateral	197,317		491,065		638,528
Not Designated as Hedging Instrument [Member] | Equity option contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	99,031	[1]	100,924	[2]	128,623	[3]
Derivative Liabilities, Notional	99,031	[1]	100,924	[2]	128,623	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	4,505		4,357		4,006
Derivative Assets, Netting Adjustments	0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral	4,505		4,357		4,006
Derivative Assets, Cash Collateral	(920)		(730)		(376)
Derviative contracts, net of cash collateral, Assets, Fair value	3,585		3,627		3,630
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	4,505		4,357		4,006
Derivative Liabilities, Netting Adjustments	0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	4,505		4,357		4,006
Derivative Liabilities, Cash Collateral	0		0		0
Derivative Liabilities, Fair Value, Net of Cash Collateral	4,505		4,357		4,006
Not Designated as Hedging Instrument [Member] | Total customer risk management programs
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	17,290,488	[1]	19,923,145	[2]	19,020,138	[3]
Derivative Liabilities, Notional	17,016,819	[1]	19,596,157	[2]	19,101,068	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	366,466		779,365		867,010
Derivative Assets, Netting Adjustments	(62,384)		(89,368)		(67,119)
Derivative Assets, Net Fair Value Before Cash Collateral	304,082		689,997		799,891
Derivative Assets, Cash Collateral	(4,884)		(10,551)		(16,686)
Derviative contracts, net of cash collateral, Assets, Fair value	299,198		679,446		783,205
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	358,174		776,093		863,433
Derivative Liabilities, Netting Adjustments	(62,384)		(89,368)		(67,119)
Derivative Liabilities, Net Fair Value Before Cash Collateral	295,790		686,725		796,314
Derivative Liabilities, Cash Collateral	(39,334)		(47,910)		(90,736)
Derivative Liabilities, Fair Value, Net of Cash Collateral	256,456		638,815		705,578
Not Designated as Hedging Instrument [Member] | Internal risk management programs
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	2,756,963	[1]	2,514,169	[2]	772,000	[3]
Derivative Liabilities, Notional	1,090,867	[1]	2,582,202	[2]	0	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	5,529		10,426		6,941
Derivative Assets, Netting Adjustments	0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral	5,529		10,426		6,941
Derivative Assets, Cash Collateral	0		0		0
Derviative contracts, net of cash collateral, Assets, Fair value	5,529		10,426		6,941
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	19,966		25,716		0
Derivative Liabilities, Netting Adjustments	0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	19,966		25,716		0
Derivative Liabilities, Cash Collateral	0		0		0
Derivative Liabilities, Fair Value, Net of Cash Collateral	$ 19,966		$ 25,716		$ 0

[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.