Fair Value of Financial Assets and Liabilities (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011		Dec. 31, 2011
Fair Value of Financial Assets and Liabilities [Abstract]
Number of years of monthly revenues or charges holder of FTRs purchased from MISO is entitled (in years)					1Y
Non-Derivative Instruments Fair Value Measurements [Abstract]
Nuclear decommissioning fund available-for-sale securities, unrealized gains	$ 109,800,000				$ 109,800,000				$ 79,800,000
Nuclear decommissioning fund available-for-sale securities, unrealized losses	76,600,000				76,600,000				87,500,000
Nuclear Decommissioning Fund [Abstract]
Cost	1,354,316,000	[1]			1,354,316,000	[1]			1,344,178,000	[2]
Other derivative instruments [Abstract]
Current derivative instruments	88,368,000				88,368,000				64,340,000
Other derivative instruments [Abstract]
Noncurrent derivative instruments	137,015,000				137,015,000				152,887,000
Other derivative instruments [Abstract]
Current derivative instruments	111,836,000				111,836,000				157,414,000
Other derivative instruments [Abstract]
Noncurrent derivative instruments	253,364,000				253,364,000				263,906,000
Investments [Abstract]
Equity investments in unconsolidated subsidiaries	100,300,000				100,300,000				92,700,000
Miscellaneous investments	34,400,000				34,400,000				34,300,000
Changes in Level 3 Nuclear Decommissioning Fund Assets [Roll Forward]
Balance	133,191,000		124,387,000		130,763,000		105,763,000
Purchases	12,920,000		52,952,000		31,615,000		99,821,000
Settlements	(19,148,000)		(93,790,000)		(37,643,000)		(121,573,000)
Gains (losses) recognized as regulatory assets and liabilities	2,450,000		(274,000)		4,678,000		(736,000)
Balance	129,413,000		83,275,000		129,413,000		83,275,000
Commodity Derivatives [Abstract]
Amount of accumulated other comprehensive gains (losses) related to commodity derivatives expected to be reclassified into earnings within the next twelve months	100,000				100,000
Financial Impact of Qualifying Fair Value Hedges [Abstract]
Derivative instruments designated as fair value hedges	0		0		0		0
Recognized gains (losses) from fair value hedges or related hedged transactions	0		0		0		0
Credit Related Contingent Features [Abstract]
Derivative instruments in a gross liability position	26,800,000				26,800,000				8,300,000
Payments required if credit ratings were downgraded below investment grade	8,800,000				8,800,000				9,300,000
Collateral posted on derivative instruments in a gross liability position	0				0				0
Collateral posted related to adequate assurance clauses in derivative contracts	0				0				0
Carrying Amount [Member]
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	10,017,997,000				10,017,997,000				9,908,435,000
Fair Value [Member]
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	11,857,476,000				11,857,476,000				11,734,798,000
Commodity Derivatives, Net [Member]
Changes in Level 3 Commodity Derivatives [Roll Forward]
Balance	5,324,000		2,332,000		12,417,000		2,392,000
Purchases	37,296,000		33,609,000		37,297,000		33,609,000
Settlements	(12,675,000)		(8,211,000)		(21,560,000)		(16,001,000)
Net transactions recorded during the period [Abstract]
Gains (losses) recognized in earnings	0	[3]	4,000	[3]	(9,000)	[3]	72,000	[3]
Gains (losses) recorded as regulatory assets and liabilities	3,844,000		(23,738,000)		5,644,000		(16,076,000)
Balance	33,789,000		3,996,000		33,789,000		3,996,000
Transfers into Level 3	0		0		0		0
Transfers out of Level 3	0		0		0		0
Cash Flow Hedges [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value gains (losses) recognized during the period in accumulated other comprehensive loss	(58,891,000)		(78,000)		(17,008,000)		311,000
Fair value gains (losses) recognized during the period in regulatory (assets) and liabilities	0		0		0		0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss	340,000		288,000		677,000		593,000
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	0		0		0		0
Pre-tax gains (losses) recognized during the period in income	0		0		0		0
Cash Flow Hedges [Member] | Interest Rate [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value gains (losses) recognized during the period in accumulated other comprehensive loss	(58,695,000)		0		(16,991,000)		0
Fair value gains (losses) recognized during the period in regulatory (assets) and liabilities	0		0		0		0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss	389,000	[4]	340,000	[4]	777,000	[4]	677,000	[4]
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	0		0		0		0
Pre-tax gains (losses) recognized during the period in income	0		0		0		0
Cash Flow Hedges [Member] | Vehicle Fuel And Other Commodity [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value gains (losses) recognized during the period in accumulated other comprehensive loss	(196,000)		(78,000)		(17,000)		311,000
Fair value gains (losses) recognized during the period in regulatory (assets) and liabilities	0		0		0		0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss	(49,000)	[5]	(52,000)	[5]	(100,000)	[5]	(84,000)	[5]
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	0		0		0		0
Pre-tax gains (losses) recognized during the period in income	0		0		0		0
Other Derivative Instruments [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value gains (losses) recognized during the period in accumulated other comprehensive loss	0		0		0		0
Fair value gains (losses) recognized during the period in regulatory (assets) and liabilities	39,059,000		735,000		29,858,000		1,966,000
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss	0		0		0		0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	(9,713,000)		(7,928,000)		63,254,000		40,571,000
Pre-tax gains (losses) recognized during the period in income	1,589,000		1,170,000		3,203,000		6,770,000
Other Derivative Instruments [Member] | Trading Commodity [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value gains (losses) recognized during the period in accumulated other comprehensive loss	0		0		0		0
Fair value gains (losses) recognized during the period in regulatory (assets) and liabilities	0		0		0		0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss	0		0		0		0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	0		0		0		0
Pre-tax gains (losses) recognized during the period in income	1,589,000	[6]	1,170,000	[6]	3,312,000	[6]	6,770,000	[6]
Other Derivative Instruments [Member] | Electric Commodity [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value gains (losses) recognized during the period in accumulated other comprehensive loss	0		0		0		0
Fair value gains (losses) recognized during the period in regulatory (assets) and liabilities	38,174,000		10,299,000		39,756,000		19,145,000
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss	0		0		0		0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	(9,713,000)	[7]	(8,666,000)	[7]	(17,685,000)	[7]	(17,554,000)	[7]
Pre-tax gains (losses) recognized during the period in income	0		0		0		0
Other Derivative Instruments [Member] | Natural Gas Commodity [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value gains (losses) recognized during the period in accumulated other comprehensive loss	0		0		0		0
Fair value gains (losses) recognized during the period in regulatory (assets) and liabilities	885,000		(9,564,000)		(9,898,000)		(17,179,000)
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss	0		0		0		0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	0		738,000	[8]	80,939,000	[8]	58,125,000	[8]
Pre-tax gains (losses) recognized during the period in income	0		0		(109,000)	[6]	0
Electric Commodity [Member]
Gross Notional Amounts of Commodity Forwards, Options and FTRs [Abstract]
Notional amount	61,499,000	[10],[9]			61,499,000	[10],[9]			38,822,000	[10],[9]
Natural Gas Commodity [Member]
Gross Notional Amounts of Commodity Forwards, Options and FTRs [Abstract]
Notional amount	8,252,000	[10],[9]			8,252,000	[10],[9]			40,736,000	[10],[9]
Vehicle Fuel Commodity [Member]
Gross Notional Amounts of Commodity Forwards, Options and FTRs [Abstract]
Notional amount	500,000	[10],[9]			500,000	[10],[9]			600,000	[10],[9]
Interest Rate Swap [Member]
Interest Rate Derivatives [Abstract]
Amount of accumulated other comprehensive gains (losses) related to interest rate derivatives expected to be reclassified into earnings within the next twelve months	(900,000)				(900,000)
Notional amount outstanding	475,000,000				475,000,000
Asset-backed Securities [Member]
Changes in Level 3 Nuclear Decommissioning Fund Assets [Roll Forward]
Balance	16,547,000		26,020,000		16,501,000		33,174,000
Purchases	0		0		0		756,000
Settlements	(9,458,000)		(5,206,000)		(9,459,000)		(13,116,000)
Gains (losses) recognized as regulatory assets and liabilities	(21,000)		190,000		26,000		190,000
Balance	7,068,000		21,004,000		7,068,000		21,004,000
Mortgage-backed Securities [Member]
Changes in Level 3 Nuclear Decommissioning Fund Assets [Roll Forward]
Balance	68,671,000		98,367,000		78,664,000		72,589,000
Purchases	7,414,000		52,952,000		14,318,000		99,065,000
Settlements	(9,690,000)		(88,584,000)		(26,418,000)		(108,457,000)
Gains (losses) recognized as regulatory assets and liabilities	(74,000)		(464,000)		(243,000)		(926,000)
Balance	66,321,000		62,271,000		66,321,000		62,271,000
Real Estate [Member]
Changes in Level 3 Nuclear Decommissioning Fund Assets [Roll Forward]
Balance	27,905,000				26,395,000
Purchases	2,271,000				3,907,000
Settlements	0				(1,766,000)
Gains (losses) recognized as regulatory assets and liabilities	2,545,000				4,185,000
Balance	32,721,000				32,721,000
Private Equity Investments [Member]
Changes in Level 3 Nuclear Decommissioning Fund Assets [Roll Forward]
Balance	20,068,000				9,203,000
Purchases	3,235,000				13,390,000
Settlements	0				0
Gains (losses) recognized as regulatory assets and liabilities	0				710,000
Balance	23,303,000				23,303,000
Fair Value Measured on a Recurring Basis [Member]
Nuclear decommissioning fund [Abstract]
Cash equivalents	24,913,000	[1]			24,913,000	[1]			26,123,000	[2]
Commingled funds	372,487,000	[1]			372,487,000	[1]			311,105,000	[2]
International equity funds	62,469,000	[1]			62,469,000	[1]			58,508,000	[2]
Private equity investments	23,303,000	[1]			23,303,000	[1]			9,203,000	[2]
Real estate	32,721,000	[1]			32,721,000	[1]			26,395,000	[2]
Debt securities [Abstract]
Government securities	119,376,000	[1]			119,376,000	[1]			117,256,000	[2]
U.S. corporate bonds	159,834,000	[1]			159,834,000	[1]			193,516,000	[2]
International corporate bonds	23,709,000	[1]			23,709,000	[1]			35,804,000	[2]
Municipal bonds	70,608,000	[1]			70,608,000	[1]			64,731,000	[2]
Asset-backed securities	7,068,000	[1]			7,068,000	[1]			16,501,000	[2]
Mortgage-backed securities	66,321,000	[1]			66,321,000	[1]			78,664,000	[2]
Equity securities [Abstract]
Common stock	424,703,000	[1]			424,703,000	[1]			398,625,000	[2]
Total	1,387,512,000	[1]			1,387,512,000	[1]			1,336,431,000	[2]
Derivatives Designated as Cash Flow Hedges [Abstract]
Vehicle fuel and other commodity	89,000				89,000				93,000
Other derivative instruments [Abstract]
Trading commodity	20,905,000				20,905,000				19,291,000
Electric commodity	33,789,000				33,789,000				11,862,000
Natural gas commodity	868,000				868,000
Total current derivative assets	55,651,000				55,651,000				31,246,000
Purchased power agreements	32,717,000	[11]			32,717,000	[11]			33,094,000	[11]
Current derivative instruments	88,368,000				88,368,000				64,340,000
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	26,000				26,000				48,000
Other derivative instruments [Abstract]
Trading commodity	31,568,000				31,568,000				31,059,000
Total noncurrent derivative assets	31,594,000				31,594,000				31,107,000
Purchased power agreements	105,421,000	[11]			105,421,000	[11]			121,780,000	[11]
Noncurrent derivative instruments	137,015,000				137,015,000				152,887,000
Derivatives designated as cash flow hedges [Abstract]
Interest rate	74,740,000				74,740,000				57,749,000
Other derivative instruments [Abstract]
Trading commodity	14,216,000				14,216,000				13,474,000
Electric commodity	0				0				143,000
Natural gas commodity	0				0				63,051,000
Total current derivative liabilities	88,956,000				88,956,000				134,417,000
Purchased power agreements	22,880,000	[11]			22,880,000	[11]			22,997,000	[11]
Current derivative instruments	111,836,000				111,836,000				157,414,000
Other derivative instruments [Abstract]
Trading commodity	16,264,000				16,264,000				15,367,000
Total noncurrent derivative liabilities	16,264,000				16,264,000				15,367,000
Purchased power agreements	237,100,000	[11]			237,100,000	[11]			248,539,000	[11]
Noncurrent derivative instruments	253,364,000				253,364,000				263,906,000
Fair Value Measured on a Recurring Basis [Member] | Level 1 [Member]
Nuclear decommissioning fund [Abstract]
Cash equivalents	15,082,000	[1]			15,082,000	[1]			7,103,000	[2]
Commingled funds	0	[1]			0	[1]			0	[2]
International equity funds	0	[1]			0	[1]			0	[2]
Private equity investments	0	[1]			0	[1]			0	[2]
Real estate	0	[1]			0	[1]			0	[2]
Debt securities [Abstract]
Government securities	0	[1]			0	[1]			0	[2]
U.S. corporate bonds	0	[1]			0	[1]			0	[2]
International corporate bonds	0	[1]			0	[1]			0	[2]
Municipal bonds	0	[1]			0	[1]			0	[2]
Asset-backed securities	0	[1]			0	[1]			0	[2]
Mortgage-backed securities	0	[1]			0	[1]			0	[2]
Equity securities [Abstract]
Common stock	424,703,000	[1]			424,703,000	[1]			398,625,000	[2]
Total	439,785,000	[1]			439,785,000	[1]			405,728,000	[2]
Derivatives Designated as Cash Flow Hedges [Abstract]
Vehicle fuel and other commodity	0				0				0
Other derivative instruments [Abstract]
Trading commodity	79,000				79,000				0
Electric commodity	0				0				0
Natural gas commodity	0				0
Total current derivative assets	79,000				79,000				0
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	0				0				0
Other derivative instruments [Abstract]
Trading commodity	0				0				0
Total noncurrent derivative assets	0				0				0
Derivatives designated as cash flow hedges [Abstract]
Interest rate	0				0				0
Other derivative instruments [Abstract]
Trading commodity	112,000				112,000				0
Electric commodity	0				0				0
Natural gas commodity	0				0				418,000
Total current derivative liabilities	112,000				112,000				418,000
Other derivative instruments [Abstract]
Trading commodity	0				0				0
Total noncurrent derivative liabilities	0				0				0
Fair Value Measured on a Recurring Basis [Member] | Level 2 [Member]
Nuclear decommissioning fund [Abstract]
Cash equivalents	9,831,000	[1]			9,831,000	[1]			19,020,000	[2]
Commingled funds	372,487,000	[1]			372,487,000	[1]			311,105,000	[2]
International equity funds	62,469,000	[1]			62,469,000	[1]			58,508,000	[2]
Private equity investments	0	[1]			0	[1]			0	[2]
Real estate	0	[1]			0	[1]			0	[2]
Debt securities [Abstract]
Government securities	119,376,000	[1]			119,376,000	[1]			117,256,000	[2]
U.S. corporate bonds	159,834,000	[1]			159,834,000	[1]			193,516,000	[2]
International corporate bonds	23,709,000	[1]			23,709,000	[1]			35,804,000	[2]
Municipal bonds	70,608,000	[1]			70,608,000	[1]			64,731,000	[2]
Asset-backed securities	0	[1]			0	[1]			0	[2]
Mortgage-backed securities	0	[1]			0	[1]			0	[2]
Equity securities [Abstract]
Common stock	0	[1]			0	[1]			0	[2]
Total	818,314,000	[1]			818,314,000	[1]			799,940,000	[2]
Derivatives Designated as Cash Flow Hedges [Abstract]
Vehicle fuel and other commodity	89,000				89,000				169,000
Other derivative instruments [Abstract]
Trading commodity	31,891,000				31,891,000				32,682,000
Electric commodity	0				0				0
Natural gas commodity	924,000				924,000
Total current derivative assets	32,904,000				32,904,000				32,851,000
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	57,000				57,000				107,000
Other derivative instruments [Abstract]
Trading commodity	36,106,000				36,106,000				36,599,000
Total noncurrent derivative assets	36,163,000				36,163,000				36,706,000
Derivatives designated as cash flow hedges [Abstract]
Interest rate	74,740,000				74,740,000				57,749,000
Other derivative instruments [Abstract]
Trading commodity	25,877,000				25,877,000				27,891,000
Electric commodity	0				0				698,000
Natural gas commodity	38,000				38,000				70,119,000
Total current derivative liabilities	100,655,000				100,655,000				156,457,000
Other derivative instruments [Abstract]
Trading commodity	20,834,000				20,834,000				20,966,000
Total noncurrent derivative liabilities	20,834,000				20,834,000				20,966,000
Fair Value Measured on a Recurring Basis [Member] | Level 3 [Member]
Nuclear decommissioning fund [Abstract]
Cash equivalents	0	[1]			0	[1]			0	[2]
Commingled funds	0	[1]			0	[1]			0	[2]
International equity funds	0	[1]			0	[1]			0	[2]
Private equity investments	23,303,000	[1]			23,303,000	[1]			9,203,000	[2]
Real estate	32,721,000	[1]			32,721,000	[1]			26,395,000	[2]
Debt securities [Abstract]
Government securities	0	[1]			0	[1]			0	[2]
U.S. corporate bonds	0	[1]			0	[1]			0	[2]
International corporate bonds	0	[1]			0	[1]			0	[2]
Municipal bonds	0	[1]			0	[1]			0	[2]
Asset-backed securities	7,068,000	[1]			7,068,000	[1]			16,501,000	[2]
Mortgage-backed securities	66,321,000	[1]			66,321,000	[1]			78,664,000	[2]
Equity securities [Abstract]
Common stock	0	[1]			0	[1]			0	[2]
Total	129,413,000	[1]			129,413,000	[1]			130,763,000	[2]
Derivatives Designated as Cash Flow Hedges [Abstract]
Vehicle fuel and other commodity	0				0				0
Other derivative instruments [Abstract]
Trading commodity	0				0				0
Electric commodity	35,664,000				35,664,000				13,333,000
Natural gas commodity	0				0
Total current derivative assets	35,664,000				35,664,000				13,333,000
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	0				0				0
Other derivative instruments [Abstract]
Trading commodity	0				0				0
Total noncurrent derivative assets	0				0				0
Derivatives designated as cash flow hedges [Abstract]
Interest rate	0				0				0
Other derivative instruments [Abstract]
Trading commodity	0				0				0
Electric commodity	1,875,000				1,875,000				916,000
Natural gas commodity	0				0				0
Total current derivative liabilities	1,875,000				1,875,000				916,000
Other derivative instruments [Abstract]
Trading commodity	0				0				0
Total noncurrent derivative liabilities	0				0				0
Fair Value Measured on a Recurring Basis [Member] | Fair Value Total [Member]
Derivatives Designated as Cash Flow Hedges [Abstract]
Vehicle fuel and other commodity	89,000				89,000				169,000
Other derivative instruments [Abstract]
Trading commodity	31,970,000				31,970,000				32,682,000
Electric commodity	35,664,000				35,664,000				13,333,000
Natural gas commodity	924,000				924,000
Total current derivative assets	68,647,000				68,647,000				46,184,000
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	57,000				57,000				107,000
Other derivative instruments [Abstract]
Trading commodity	36,106,000				36,106,000				36,599,000
Total noncurrent derivative assets	36,163,000				36,163,000				36,706,000
Derivatives designated as cash flow hedges [Abstract]
Interest rate	74,740,000				74,740,000				57,749,000
Other derivative instruments [Abstract]
Trading commodity	25,989,000				25,989,000				27,891,000
Electric commodity	1,875,000				1,875,000				1,614,000
Natural gas commodity	38,000				38,000				70,537,000
Total current derivative liabilities	102,642,000				102,642,000				157,791,000
Other derivative instruments [Abstract]
Trading commodity	20,834,000				20,834,000				20,966,000
Total noncurrent derivative liabilities	20,834,000				20,834,000				20,966,000
Fair Value Measured on a Recurring Basis [Member] | Counterparty Netting [Member]
Derivatives Designated as Cash Flow Hedges [Abstract]
Vehicle fuel and other commodity	0	[12]			0	[12]			(76,000)	[12]
Other derivative instruments [Abstract]
Trading commodity	(11,065,000)	[12]			(11,065,000)	[12]			(13,391,000)	[12]
Electric commodity	(1,875,000)	[12]			(1,875,000)	[12]			(1,471,000)	[12]
Natural gas commodity	(56,000)	[12]			(56,000)	[12]
Total current derivative assets	(12,996,000)	[12]			(12,996,000)	[12]			(14,938,000)	[12]
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	(31,000)	[12]			(31,000)	[12]			(59,000)	[12]
Other derivative instruments [Abstract]
Trading commodity	(4,538,000)	[12]			(4,538,000)	[12]			(5,540,000)	[12]
Total noncurrent derivative assets	(4,569,000)	[12]			(4,569,000)	[12]			(5,599,000)	[12]
Derivatives designated as cash flow hedges [Abstract]
Interest rate	0	[12]			0	[12]			0	[12]
Other derivative instruments [Abstract]
Trading commodity	(11,773,000)	[12]			(11,773,000)	[12]			(14,417,000)	[12]
Electric commodity	(1,875,000)	[12]			(1,875,000)	[12]			(1,471,000)	[12]
Natural gas commodity	(38,000)	[12]			(38,000)	[12]			(7,486,000)	[12]
Total current derivative liabilities	(13,686,000)	[12]			(13,686,000)	[12]			(23,374,000)	[12]
Other derivative instruments [Abstract]
Trading commodity	(4,570,000)	[12]			(4,570,000)	[12]			(5,599,000)	[12]
Total noncurrent derivative liabilities	(4,570,000)	[12]			(4,570,000)	[12]			(5,599,000)	[12]
Cash Equivalents [Member]
Nuclear Decommissioning Fund [Abstract]
Cost	24,913,000	[1]			24,913,000	[1]			26,123,000	[2]
Commingled Funds [Member]
Nuclear Decommissioning Fund [Abstract]
Cost	375,222,000	[1]			375,222,000	[1]			320,798,000	[2]
International Equity Funds [Member]
Nuclear Decommissioning Fund [Abstract]
Cost	65,712,000	[1]			65,712,000	[1]			63,781,000	[2]
Private Equity Investments [Member]
Nuclear Decommissioning Fund [Abstract]
Cost	22,593,000	[1]			22,593,000	[1]			9,203,000	[2]
Real Estate [Member]
Nuclear Decommissioning Fund [Abstract]
Cost	28,536,000	[1]			28,536,000	[1]			24,768,000	[2]
Debt Securities [Member]
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	104,694,000				104,694,000
Due in 1 to 5 Years	51,575,000				51,575,000
Due in 5 to 10 Years	155,364,000				155,364,000
Due after 10 Years	135,283,000				135,283,000
Total	446,916,000				446,916,000
Government Securities [Member]
Nuclear Decommissioning Fund [Abstract]
Cost	118,378,000	[1]			118,378,000	[1]			116,490,000	[2]
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	104,694,000				104,694,000
Due in 1 to 5 Years	79,000				79,000
Due in 5 to 10 Years	3,648,000				3,648,000
Due after 10 Years	10,955,000				10,955,000
Total	119,376,000				119,376,000
U.S. Corporate Bonds [Member]
Nuclear Decommissioning Fund [Abstract]
Cost	151,444,000	[1]			151,444,000	[1]			187,083,000	[2]
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0				0
Due in 1 to 5 Years	40,032,000				40,032,000
Due in 5 to 10 Years	103,834,000				103,834,000
Due after 10 Years	15,968,000				15,968,000
Total	159,834,000				159,834,000
International Corporate Bonds [Member]
Nuclear Decommissioning Fund [Abstract]
Cost	22,782,000	[1]			22,782,000	[1]			35,198,000	[2]
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0				0
Due in 1 to 5 Years	6,481,000				6,481,000
Due in 5 to 10 Years	17,228,000				17,228,000
Due after 10 Years	0				0
Total	23,709,000				23,709,000
Municipal Bonds [Member]
Nuclear Decommissioning Fund [Abstract]
Cost	66,769,000	[1]			66,769,000	[1]			60,469,000	[2]
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0				0
Due in 1 to 5 Years	0				0
Due in 5 to 10 Years	27,692,000				27,692,000
Due after 10 Years	42,916,000				42,916,000
Total	70,608,000				70,608,000
Asset-backed Securities [Member]
Nuclear Decommissioning Fund [Abstract]
Cost	7,057,000	[1]			7,057,000	[1]			16,516,000	[2]
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0				0
Due in 1 to 5 Years	4,983,000				4,983,000
Due in 5 to 10 Years	2,085,000				2,085,000
Due after 10 Years	0				0
Total	7,068,000				7,068,000
Mortgage-backed Securities [Member]
Nuclear Decommissioning Fund [Abstract]
Cost	63,526,000	[1]			63,526,000	[1]			75,627,000	[2]
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0				0
Due in 1 to 5 Years	0				0
Due in 5 to 10 Years	877,000				877,000
Due after 10 Years	65,444,000				65,444,000
Total	66,321,000				66,321,000
Common Stock [Member]
Nuclear Decommissioning Fund [Abstract]
Cost	$ 407,384,000	[1]			$ 407,384,000	[1]			$ 408,122,000	[2]

[1] Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $100.3 million of equity investments in unconsolidated subsidiaries and $34.4 million of miscellaneous investments.

[2] Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $92.7 million of equity investments in unconsolidated subsidiaries and $34.3 million of miscellaneous investments.

[3] These amounts relate to commodity derivatives held at the end of the period.

[4] Recorded to interest charges.

[5] Recorded to operating and maintenance (O&M) expenses.

[6] Recorded to electric operating revenues. Portions of these gains and losses are subject to sharing with electric customers through margin-sharing mechanisms and deducted from gross revenue, as appropriate.

[7] Recorded to electric fuel and purchased power. These derivative settlement gains and losses are shared with electric customers through fuel and purchased energy cost-recovery mechanisms, and reclassified out of income as regulatory assets or liabilities, as appropriate.

[8] Recorded to cost of natural gas sold and transported. These derivative settlement gains and losses are shared with natural gas customers through purchased natural gas cost-recovery mechanisms, and reclassified out of income as regulatory assets or liabilities, as appropriate.

[9] Amounts are not reflective of net positions in the underlying commodities.

[10] Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.

[11] In 2003, as a result of implementing new guidance on the normal purchase exception for derivative accounting, Xcel Energy began recording several long-term purchased power agreements at fair value due to accounting requirements related to underlying price adjustments. As these purchases are recovered through normal regulatory recovery mechanisms in the respective jurisdictions, the changes in fair value for these contracts were offset by regulatory assets and liabilities. During 2006, Xcel Energy qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

[12] The accounting guidance for derivatives and hedging permits the netting of receivables and payables for derivatives and related collateral amounts when a legally enforceable master netting agreement exists between Xcel Energy and a counterparty. A master netting agreement is an agreement between two parties who have multiple contracts with each other that provides for the net settlement of all contracts in the event of default on or termination of any one contract.