Derivatives, Fair Value of Derivatives Contracts (Details) (USD $)	Jun. 30, 2011		Dec. 31, 2010		Jun. 30, 2010
Notional Amount of Derivatives [Abstract]
Derivative Asset, Notional Amount, Gross Basis	$ 10,605,839,000	[1]	$ 14,091,727,000	[1]	$ 12,361,822,000	[1]
Derivative Liability, Notional Amount, Gross Basis	10,584,538,000	[1]	14,038,235,000	[1]	12,415,819,000	[1]
Derivative Asset, Fair Value, Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	378,687,000		498,443,000		603,356,000
Derivative Asset, Fair Value, Net Asset	229,887,000		270,445,000		334,576,000
Derivative Liability, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	374,177,000		497,388,000		599,409,000
Derivative Liability, Fair Value, Net Liability	173,917,000		215,420,000		299,851,000
Increase in cash margin obligation for derivative holdings with a decrease in credit rating from A1 to below investment grade	70,000,000
Interest Rate Contract [Member]
Notional Amount of Derivatives [Abstract]
Derivative Asset, Notional Amount, Gross Basis	8,258,239,000	[1]	11,664,409,000	[1]	9,128,247,000	[1]
Derivative Liability, Notional Amount, Gross Basis	8,096,551,000	[1]	11,524,077,000	[1]	8,975,646,000	[1]
Derivative Asset, Fair Value, Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	114,945,000		235,961,000		199,965,000
Derivative Asset, Fair Value, Net Asset	91,439,000	[2]	141,279,000	[2]	153,044,000	[2]
Derivative Liability, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	113,534,000		233,421,000		198,807,000
Derivative Liability, Fair Value, Net Liability	90,028,000	[2]	138,739,000	[2]	151,858,000	[2]
Energy Contracts [Member]
Notional Amount of Derivatives [Abstract]
Derivative Asset, Notional Amount, Gross Basis	1,917,521,000	[1]	1,914,519,000	[1]	2,667,481,000	[1]
Derivative Liability, Notional Amount, Gross Basis	2,094,878,000	[1]	2,103,923,000	[1]	3,007,643,000	[1]
Derivative Asset, Fair Value, Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	158,922,000		188,655,000		327,577,000
Derivative Asset, Fair Value, Net Asset	51,820,000	[2]	76,746,000	[2]	119,537,000	[2]
Derivative Liability, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	157,998,000		191,075,000		332,804,000
Derivative Liability, Fair Value, Net Liability	50,896,000	[2]	79,166,000	[2]	124,764,000	[2]
Agriculture Contracts [Member]
Notional Amount of Derivatives [Abstract]
Derivative Asset, Notional Amount, Gross Basis	125,644,000	[1]	183,250,000	[1]	236,113,000	[1]
Derivative Liability, Notional Amount, Gross Basis	132,573,000	[1]	186,709,000	[1]	242,192,000	[1]
Derivative Asset, Fair Value, Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	6,025,000		10,616,000		6,882,000
Derivative Asset, Fair Value, Net Asset	1,847,000	[2]	4,226,000	[2]	936,000	[2]
Derivative Liability, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	5,961,000		10,534,000		6,607,000
Derivative Liability, Fair Value, Net Liability	1,783,000	[2]	4,144,000	[2]	657,000	[2]
Foreign Exchange Contract [Member]
Notional Amount of Derivatives [Abstract]
Derivative Asset, Notional Amount, Gross Basis	78,471,000	[1]	45,014,000	[1]	54,241,000	[1]
Derivative Liability, Notional Amount, Gross Basis	78,572,000	[1]	45,014,000	[1]	54,241,000	[1]
Derivative Asset, Fair Value, Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	78,471,000		45,014,000		54,241,000
Derivative Asset, Fair Value, Net Asset	78,471,000	[2]	45,014,000	[2]	54,241,000	[2]
Derivative Liability, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	78,572,000		45,014,000		54,241,000
Derivative Liability, Fair Value, Net Liability	78,572,000	[2]	45,014,000	[2]	54,241,000	[2]
Equity Swap [Member]
Notional Amount of Derivatives [Abstract]
Derivative Asset, Notional Amount, Gross Basis	181,964,000	[1]	160,535,000	[1]	107,740,000	[1]
Derivative Liability, Notional Amount, Gross Basis	181,964,000	[1]	160,535,000	[1]	107,740,000	[1]
Derivative Asset, Fair Value, Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	18,112,000		16,247,000		6,854,000
Derivative Asset, Fair Value, Net Asset	18,112,000	[2]	16,247,000	[2]	6,854,000	[2]
Derivative Liability, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	18,112,000		16,247,000		6,854,000
Derivative Liability, Fair Value, Net Liability	18,112,000	[2]	16,247,000	[2]	6,854,000	[2]
Customer Derivative Before Cash Collateral [Member]
Notional Amount of Derivatives [Abstract]
Derivative Asset, Notional Amount, Gross Basis	10,561,839,000	[1]	13,967,727,000	[1]	12,193,822,000	[1]
Derivative Liability, Notional Amount, Gross Basis	10,584,538,000	[1]	14,020,258,000	[1]	12,387,462,000	[1]
Derivative Asset, Fair Value, Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	376,475,000		496,493,000		595,519,000
Derivative Asset, Fair Value, Net Asset	241,689,000	[2]	283,512,000	[2]	334,612,000	[2]
Derivative Liability, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	374,177,000		496,291,000		599,313,000
Derivative Liability, Fair Value, Net Liability	239,391,000	[2]	283,310,000	[2]	338,374,000	[2]
Cash Collateral [Member]
Notional Amount of Derivatives [Abstract]
Derivative Asset, Notional Amount, Gross Basis	0	[1]	0	[1]	0	[1]
Derivative Liability, Notional Amount, Gross Basis	0	[1]	0	[1]	0	[1]
Derivative Asset, Fair Value, Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	0		0		0
Derivative Asset, Fair Value, Net Asset	(14,014,000)	[2]	(15,017,000)	[2]	(7,873,000)	[2]
Derivative Liability, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	0		0		0
Derivative Liability, Fair Value, Net Liability	(65,474,000)	[2]	(68,987,000)	[2]	(38,619,000)	[2]
Total Customer Derivatives [Member]
Notional Amount of Derivatives [Abstract]
Derivative Asset, Notional Amount, Gross Basis	10,561,839,000	[1]	13,967,727,000	[1]	12,193,822,000	[1]
Derivative Liability, Notional Amount, Gross Basis	10,584,538,000	[1]	14,020,258,000	[1]	12,387,462,000	[1]
Derivative Asset, Fair Value, Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	376,475,000		496,493,000		595,519,000
Derivative Asset, Fair Value, Net Asset	227,675,000	[2]	268,495,000	[2]	326,739,000	[2]
Derivative Liability, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	374,177,000		496,291,000		599,313,000
Derivative Liability, Fair Value, Net Liability	173,917,000	[2]	214,323,000	[2]	299,755,000	[2]
Interest Rate Risk Management Program [Member]
Notional Amount of Derivatives [Abstract]
Derivative Asset, Notional Amount, Gross Basis	44,000,000	[1]	124,000,000	[1]	168,000,000	[1]
Derivative Liability, Notional Amount, Gross Basis	0	[1]	17,977,000	[1]	28,357,000	[1]
Derivative Asset, Fair Value, Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	2,212,000		1,950,000		7,837,000
Derivative Asset, Fair Value, Net Asset	2,212,000	[2]	1,950,000	[2]	7,837,000	[2]
Derivative Liability, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	0		1,097,000		96,000
Derivative Liability, Fair Value, Net Liability	$ 0	[2]	$ 1,097,000	[2]	$ 96,000	[2]

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

[2] Derivative contracts are recorded on a net basis in the balance sheet in recognition of master netting agreements that enable the Company to settle all derivative positions with a given counterparty in total and to offset the net derivative position with the related cash collateral.