Derivatives, Fair Value of Derivatives Contracts (Details) - USD ($) $ in Thousands	Jun. 30, 2018		Dec. 31, 2017		Jun. 30, 2017
Derivative Assets, Fair Value, Net [Abstract]
Derviative contracts, net of cash collateral, Assets, Fair value	$ 373,373		$ 220,502		$ 280,289
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Net of Cash Collateral	234,856		171,963		285,819
Not Designated as Hedging Instrument [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	28,203,682	[1]	20,038,522	[2]	29,511,796	[3]
Derivative Liabilities, Notional	29,551,215	[1]	20,186,467	[2]	27,125,429	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	486,962		301,052		355,296
Derivative Assets, Netting Adjustments	(100,160)		(74,022)		(50,607)
Derivative Assets, Net Fair Value Before Cash Collateral	386,802		227,030		304,689
Derivative Assets, Cash Collateral	(13,428)		(6,528)		(24,400)
Derviative contracts, net of cash collateral, Assets, Fair value	373,374		220,502		280,289
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	484,768		302,405		357,521
Derivative Liabilities, Netting Adjustments	(100,160)		(74,022)		(50,607)
Derivative Liabilities, Net Fair Value Before Cash Collateral	384,608		228,383		306,914
Derivative Liabilities, Cash Collateral	(149,752)		(56,420)		(21,095)
Derivative Liabilities, Fair Value, Net of Cash Collateral	234,856		171,963		285,819
Not Designated as Hedging Instrument [Member] | To-be-announced residential mortgage-backed securities
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	15,027,678	[1]	12,347,542	[2]	16,174,687	[3]
Derivative Liabilities, Notional	14,443,478	[1]	11,537,742	[2]	16,174,687	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	52,681		23,606		57,948
Derivative Assets, Netting Adjustments	(17,382)		(18,096)		(29,034)
Derivative Assets, Net Fair Value Before Cash Collateral	35,299		5,510		28,914
Derivative Assets, Cash Collateral	0		0		0
Derviative contracts, net of cash collateral, Assets, Fair value	35,299		5,510		28,914
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	49,343		20,367		53,829
Derivative Liabilities, Netting Adjustments	(17,382)		(18,096)		(29,034)
Derivative Liabilities, Net Fair Value Before Cash Collateral	31,961		2,271		24,795
Derivative Liabilities, Cash Collateral	(31,808)		(704)		0
Derivative Liabilities, Fair Value, Net of Cash Collateral	153		1,567		24,795
Not Designated as Hedging Instrument [Member] | Interest rate swaps
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	1,745,237	[1]	1,478,944	[2]	1,450,193	[3]
Derivative Liabilities, Notional	1,745,237	[1]	1,478,944	[2]	1,450,193	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	43,040		28,278		29,932
Derivative Assets, Netting Adjustments	(2,193)		0		0
Derivative Assets, Net Fair Value Before Cash Collateral	40,847		28,278		29,932
Derivative Assets, Cash Collateral	(11,737)		(4,964)		(2,206)
Derviative contracts, net of cash collateral, Assets, Fair value	29,110		23,314		27,726
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	43,043		28,298		29,982
Derivative Liabilities, Netting Adjustments	(2,193)		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	40,850		28,298		29,982
Derivative Liabilities, Cash Collateral	(4,946)		(12,896)		(15,396)
Derivative Liabilities, Fair Value, Net of Cash Collateral	35,904		15,402		14,586
Not Designated as Hedging Instrument [Member] | Energy contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	1,465,826	[1]	1,190,067	[2]	891,480	[3]
Derivative Liabilities, Notional	1,434,980	[1]	1,166,924	[2]	874,625	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	200,640		103,044		56,824
Derivative Assets, Netting Adjustments	(69,991)		(47,873)		(20,546)
Derivative Assets, Net Fair Value Before Cash Collateral	130,649		55,171		36,278
Derivative Assets, Cash Collateral	0		(196)		(21,267)
Derviative contracts, net of cash collateral, Assets, Fair value	130,649		54,975		15,011
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	199,119		101,603		53,895
Derivative Liabilities, Netting Adjustments	(69,990)		(47,873)		(20,546)
Derivative Liabilities, Net Fair Value Before Cash Collateral	129,129		53,730		33,349
Derivative Liabilities, Cash Collateral	(112,481)		(42,767)		0
Derivative Liabilities, Fair Value, Net of Cash Collateral	16,648		10,963		33,349
Not Designated as Hedging Instrument [Member] | Agricultural contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	23,508	[1]	53,238	[2]	45,250	[3]
Derivative Liabilities, Notional	23,496	[1]	48,552	[2]	45,262	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	1,164		1,576		3,541
Derivative Assets, Netting Adjustments	(181)		(960)		(1,027)
Derivative Assets, Net Fair Value Before Cash Collateral	983		616		2,514
Derivative Assets, Cash Collateral	(741)		0		0
Derviative contracts, net of cash collateral, Assets, Fair value	242		616		2,514
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	1,142		1,551		3,538
Derivative Liabilities, Netting Adjustments	(181)		(960)		(1,027)
Derivative Liabilities, Net Fair Value Before Cash Collateral	961		591		2,511
Derivative Liabilities, Cash Collateral	0		0		(2,511)
Derivative Liabilities, Fair Value, Net of Cash Collateral	961		591		0
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	174,851	[1]	132,397	[2]	169,529	[3]
Derivative Liabilities, Notional	161,567	[1]	126,251	[2]	169,553	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	170,556		129,551		162,429
Derivative Assets, Netting Adjustments	0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral	170,556		129,551		162,429
Derivative Assets, Cash Collateral	(290)		(448)		(7)
Derviative contracts, net of cash collateral, Assets, Fair value	170,266		129,103		162,422
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	157,174		123,321		162,276
Derivative Liabilities, Netting Adjustments	(1)		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	157,173		123,321		162,276
Derivative Liabilities, Cash Collateral	(517)		(53)		(3,188)
Derivative Liabilities, Fair Value, Net of Cash Collateral	156,656		123,268		159,088
Not Designated as Hedging Instrument [Member] | Equity option contracts
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	93,943	[1]	99,633	[2]	100,159	[3]
Derivative Liabilities, Notional	93,943	[1]	99,633	[2]	100,159	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	4,121		5,503		4,437
Derivative Assets, Netting Adjustments	0		0		0
Derivative Assets, Net Fair Value Before Cash Collateral	4,121		5,503		4,437
Derivative Assets, Cash Collateral	(660)		(920)		(920)
Derviative contracts, net of cash collateral, Assets, Fair value	3,461		4,583		3,517
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	4,121		5,503		4,437
Derivative Liabilities, Netting Adjustments	0		0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	4,121		5,503		4,437
Derivative Liabilities, Cash Collateral	0		0		0
Derivative Liabilities, Fair Value, Net of Cash Collateral	4,121		5,503		4,437
Not Designated as Hedging Instrument [Member] | Total customer risk management programs
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	18,531,043	[1]	15,301,821	[2]	18,831,298	[3]
Derivative Liabilities, Notional	17,902,701	[1]	14,458,046	[2]	18,814,479	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	472,202		291,558		315,111
Derivative Assets, Netting Adjustments	(89,747)		(66,929)		(50,607)
Derivative Assets, Net Fair Value Before Cash Collateral	382,455		224,629		264,504
Derivative Assets, Cash Collateral	(13,428)		(6,528)		(24,400)
Derviative contracts, net of cash collateral, Assets, Fair value	369,027		218,101		240,104
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	453,942		280,643		307,957
Derivative Liabilities, Netting Adjustments	(89,747)		(66,929)		(50,607)
Derivative Liabilities, Net Fair Value Before Cash Collateral	364,195		213,714		257,350
Derivative Liabilities, Cash Collateral	(149,752)		(56,420)		(21,095)
Derivative Liabilities, Fair Value, Net of Cash Collateral	214,443		157,294		236,255
Not Designated as Hedging Instrument [Member] | Internal risk management programs
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	9,672,639	[1]	4,736,701	[2]	10,680,498	[3]
Derivative Liabilities, Notional	11,648,514	[1]	5,728,421	[2]	8,310,950	[3]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	14,760		9,494		40,185
Derivative Assets, Netting Adjustments	(10,413)		(7,093)		0
Derivative Assets, Net Fair Value Before Cash Collateral	4,347		2,401		40,185
Derivative Assets, Cash Collateral	0		0		0
Derviative contracts, net of cash collateral, Assets, Fair value	4,347		2,401		40,185
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Gross Fair Value	30,826		21,762		49,564
Derivative Liabilities, Netting Adjustments	(10,413)		(7,093)		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	20,413		14,669		49,564
Derivative Liabilities, Cash Collateral	0		0		0
Derivative Liabilities, Fair Value, Net of Cash Collateral	$ 20,413		$ 14,669		$ 49,564

[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.