Derivatives, Fair Value of Derivatives Contracts (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
Derivative Assets, Fair Value, Net [Abstract]
Derivative contracts, net of cash margin, Assets, Fair Value	$ 265,012,000		$ 338,106,000
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	247,185,000		283,589,000
Increase in cash margin obligation for derivative holdings with a decrease in credit rating from A1 to below investment grade	26,000,000
Not Designated as Hedging Instrument [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	13,812,049,000	[1]	16,188,105,000	[1]
Derivative Liabilities, Notional	13,974,098,000	[1]	16,547,182,000	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	351,683,000		404,875,000
Derivative Assets, Netting Adjustments	(77,746,000)		(63,305,000)
Derivative Assets, Net Fair Value Before Cash Collateral	273,937,000		341,570,000
Derivative Assets, Fair Value, Cash Collateral	(8,925,000)		(3,464,000)
Derivative contracts, net of cash margin, Assets, Fair Value	265,012,000		338,106,000
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	349,133,000		396,263,000
Derivative Liabilities, Netting Adjustments	(77,746,000)		(63,305,000)
Derivative Liabilities, Net Fair Value Before Cash Collateral	271,387,000		332,958,000
Derivative Liabilities, Fair Value, Cash Collateral	(24,202,000)		(49,369,000)
Derivative contracts, net of cash margin, Liabilities, Fair Value	247,185,000		283,589,000
Not Designated as Hedging Instrument [Member] | To-be-announced residential mortgage-backed securities [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	10,817,159,000	[1]	12,850,805,000	[1]
Derivative Liabilities, Notional	10,982,049,000	[1]	13,239,078,000	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	102,921,000		46,113,000
Derivative Assets, Netting Adjustments	(46,623,000)		(15,656,000)
Derivative Assets, Net Fair Value Before Cash Collateral	56,298,000		30,457,000
Derivative Assets, Fair Value, Cash Collateral	0		0
Derivative contracts, net of cash margin, Assets, Fair Value	56,298,000		30,457,000
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	99,830,000		43,064,000
Derivative Liabilities, Netting Adjustments	(46,623,000)		(15,656,000)
Derivative Liabilities, Net Fair Value Before Cash Collateral	53,207,000		27,408,000
Derivative Liabilities, Fair Value, Cash Collateral	0		(15,467,000)
Derivative contracts, net of cash margin, Liabilities, Fair Value	53,207,000		11,941,000
Not Designated as Hedging Instrument [Member] | Interest rate swaps [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	1,283,379,000	[1]	1,319,827,000	[1]
Derivative Liabilities, Notional	1,283,379,000	[1]	1,319,827,000	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	44,124,000		72,201,000
Derivative Assets, Netting Adjustments	0		0
Derivative Assets, Net Fair Value Before Cash Collateral	44,124,000		72,201,000
Derivative Assets, Fair Value, Cash Collateral	(731,000)		0
Derivative contracts, net of cash margin, Assets, Fair Value	43,393,000		72,201,000
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	44,377,000		72,724,000
Derivative Liabilities, Netting Adjustments	0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	44,377,000		72,724,000
Derivative Liabilities, Fair Value, Cash Collateral	(17,853,000)		(31,945,000)
Derivative contracts, net of cash margin, Liabilities, Fair Value	26,524,000		40,779,000
Not Designated as Hedging Instrument [Member] | Energy contracts [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	1,263,266,000	[1]	1,346,780,000	[1]
Derivative Liabilities, Notional	1,216,426,000	[1]	1,334,349,000	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	48,078,000		82,349,000
Derivative Assets, Netting Adjustments	(29,957,000)		(44,485,000)
Derivative Assets, Net Fair Value Before Cash Collateral	18,121,000		37,864,000
Derivative Assets, Fair Value, Cash Collateral	(2,575,000)		(3,464,000)
Derivative contracts, net of cash margin, Assets, Fair Value	15,546,000		34,400,000
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	46,095,000		83,654,000
Derivative Liabilities, Netting Adjustments	(29,957,000)		(44,485,000)
Derivative Liabilities, Net Fair Value Before Cash Collateral	16,138,000		39,169,000
Derivative Liabilities, Fair Value, Cash Collateral	(6,055,000)		(1,769,000)
Derivative contracts, net of cash margin, Liabilities, Fair Value	10,083,000		37,400,000
Not Designated as Hedging Instrument [Member] | Agricultural contracts [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	100,886,000	[1]	212,434,000	[1]
Derivative Liabilities, Notional	99,191,000	[1]	212,135,000	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	2,060,000		3,638,000
Derivative Assets, Netting Adjustments	(1,166,000)		(3,164,000)
Derivative Assets, Net Fair Value Before Cash Collateral	894,000		474,000
Derivative Assets, Fair Value, Cash Collateral	0		0
Derivative contracts, net of cash margin, Assets, Fair Value	894,000		474,000
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	2,009,000		3,571,000
Derivative Liabilities, Netting Adjustments	(1,166,000)		(3,164,000)
Derivative Liabilities, Net Fair Value Before Cash Collateral	843,000		407,000
Derivative Liabilities, Fair Value, Cash Collateral	0		(188,000)
Derivative contracts, net of cash margin, Liabilities, Fair Value	843,000		219,000
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	136,543,000	[1]	180,318,000	[1]
Derivative Liabilities, Notional	135,237,000	[1]	179,852,000	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	136,543,000		180,318,000
Derivative Assets, Netting Adjustments	0		0
Derivative Assets, Net Fair Value Before Cash Collateral	136,543,000		180,318,000
Derivative Assets, Fair Value, Cash Collateral	(2,147,000)		0
Derivative contracts, net of cash margin, Assets, Fair Value	134,396,000		180,318,000
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	135,237,000		179,852,000
Derivative Liabilities, Netting Adjustments	0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	135,237,000		179,852,000
Derivative Liabilities, Fair Value, Cash Collateral	(294,000)		0
Derivative contracts, net of cash margin, Liabilities, Fair Value	134,943,000		179,852,000
Not Designated as Hedging Instrument [Member] | Equity option contracts [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	210,816,000	[1]	211,941,000	[1]
Derivative Liabilities, Notional	210,816,000	[1]	211,941,000	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	17,957,000		12,593,000
Derivative Assets, Netting Adjustments	0		0
Derivative Assets, Net Fair Value Before Cash Collateral	17,957,000		12,593,000
Derivative Assets, Fair Value, Cash Collateral	(3,472,000)		0
Derivative contracts, net of cash margin, Assets, Fair Value	14,485,000		12,593,000
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	17,957,000		12,593,000
Derivative Liabilities, Netting Adjustments	0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	17,957,000		12,593,000
Derivative Liabilities, Fair Value, Cash Collateral	0		0
Derivative contracts, net of cash margin, Liabilities, Fair Value	17,957,000		12,593,000
Not Designated as Hedging Instrument [Member] | Customer risk management programs [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	13,812,049,000	[1]	16,122,105,000	[1]
Derivative Liabilities, Notional	13,927,098,000	[1]	16,497,182,000	[1]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	351,683,000		397,212,000
Derivative Assets, Netting Adjustments	(77,746,000)		(63,305,000)
Derivative Assets, Net Fair Value Before Cash Collateral	273,937,000		333,907,000
Derivative Assets, Fair Value, Cash Collateral	(8,925,000)		(3,464,000)
Derivative contracts, net of cash margin, Assets, Fair Value	265,012,000		330,443,000
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	345,505,000		395,458,000
Derivative Liabilities, Netting Adjustments	(77,746,000)		(63,305,000)
Derivative Liabilities, Net Fair Value Before Cash Collateral	267,759,000		332,153,000
Derivative Liabilities, Fair Value, Cash Collateral	(24,202,000)		(49,369,000)
Derivative contracts, net of cash margin, Liabilities, Fair Value	243,557,000		282,784,000
Not Designated as Hedging Instrument [Member] | Interest rate risk management program [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	0	[1]	66,000,000	[1]
Derivative Liabilities, Notional	47,000,000	[1]	50,000,000	[1]
Derivative, Notional Amount	47,000,000
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	0		7,663,000
Derivative Assets, Netting Adjustments	0		0
Derivative Assets, Net Fair Value Before Cash Collateral	0		7,663,000
Derivative Assets, Fair Value, Cash Collateral	0		0
Derivative contracts, net of cash margin, Assets, Fair Value	0		7,663,000
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	3,628,000		805,000
Derivative Liabilities, Netting Adjustments	0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	3,628,000		805,000
Derivative Liabilities, Fair Value, Cash Collateral	0		0
Derivative contracts, net of cash margin, Liabilities, Fair Value	$ 3,628,000		$ 805,000

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