Fair Value of Financial Assets and Liabilities (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Non-Derivative Instruments Fair Value Measurements [Abstract]
Nuclear decommissioning fund available-for-sale securities, unrealized gains	$ 79,800,000		$ 82,500,000
Nuclear decommissioning fund available-for-sale securities, unrealized losses	87,500,000		65,200,000
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Amortized cost basis	1,344,178,000	[1]	1,333,373,000	[2]
Other derivative instruments [Abstract]
Current derivative instruments	64,340,000		54,079,000
Other derivative instruments [Abstract]
Noncurrent derivative instruments	152,887,000		184,026,000
Other derivative instruments [Abstract]
Current derivative instruments	157,414,000		61,745,000
Other derivative instruments [Abstract]
Noncurrent derivative instruments	263,906,000		285,986,000
Investments [Abstract]
Equity investments in unconsolidated subsidiaries	92,700,000		97,600,000
Miscellaneous investments	34,300,000		28,200,000
Changes in Level 3 Nuclear Decommissioning Fund Assets [Roll Forward]
Balance	105,763,000		93,107,000		109,423,000
Purchases	219,177,000		102,368,000		25,214,000
Settlements	(193,694,000)		(93,579,000)		(53,570,000)
Gains (losses) recognized as regulatory assets and liabilities	(483,000)		3,867,000		12,040,000
Balance	130,763,000		105,763,000		93,107,000
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	200,000
Number of months for which accumulated OCI related to commodity derivative cash flow hedges are expected to be reclassified into earnings (in months)	12M
Financial Impact of Qualifying Cash Flow Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Accumulated other comprehensive loss related to cash flow hedges	(8,094,000)		(6,435,000)		(13,113,000)
After-tax net unrealized losses related to derivatives accounted for as hedges	(38,292,000)		(4,289,000)		(710,000)
After-tax net realized losses on derivative transactions reclassified into earnings	648,000		2,630,000		7,388,000
Accumulated other comprehensive loss related to cash flow hedges	(45,738,000)		(8,094,000)		(6,435,000)
Financial Impact of Qualifying Fair Value Hedges [Abstract]
Derivative instruments designated as fair value hedges	0		0
Recognized gains (losses) from fair value hedges or related hedged transactions	0		0
Credit Related Contingent Features [Abstract]
Derivative instruments in a gross liability position	8,300,000		5,600,000
Payments required if credit ratings were downgraded below investment grade	9,300,000		9,800,000
Collateral posted on derivative instruments in a gross liability position	0		0
Collateral posted related to adequate assurance clauses in derivative contracts	0		0
Carrying Amount [Member]
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	9,908,435,000		9,318,559,000
Fair Value [Member]
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	11,734,798,000		10,224,845,000
Commodity Derivatives, Net [Member]
Trading commodity derivatives not designated as cash flow hedges [Abstract]
Current assets			7,271,000
Noncurrent assets			26,438,000
Current liabilities			(4,115,000)
Noncurrent liabilities			(16,069,000)
Total	0		13,525,000		(1,280,000)
Fair Value Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance	2,392,000		28,042,000		23,221,000
Purchases	33,609,000		10,813,000		9,077,000
Settlements	(36,555,000)		(25,261,000)		(18,316,000)
Transfers (out of) into Level 3	0		(13,525,000)		1,280,000
Gains recognized in earnings	69,000	[3]	6,237,000	[3]	8,228,000	[3]
Gains (losses) recognized as regulatory assets and liabilities	12,902,000		(3,914,000)		4,552,000
Balance	12,417,000		2,392,000		28,042,000
Cash Flow Hedges [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value changes recognized during the period in other comprehensive income (losses)	(63,378,000)		(7,448,000)
Fair value changes recognized during the period in regulatory assets and liabilities	0		0
Pre-tax amounts reclassified into income during the period from accumulated other comprehensive income	1,246,000		4,581,000
Pre-tax amounts reclassified into income during the period from regulatory assets and liabilities	0		0
Pre-tax gains (losses) recognized during the period in income	0		0
Cash Flow Hedges [Member] | Interest Rate [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value changes recognized during the period in other comprehensive income (losses)	(63,573,000)		(7,210,000)
Fair value changes recognized during the period in regulatory assets and liabilities	0		0
Pre-tax amounts reclassified into income during the period from accumulated other comprehensive income	1,424,000	[4]	1,107,000	[4]
Pre-tax amounts reclassified into income during the period from regulatory assets and liabilities	0		0
Pre-tax gains (losses) recognized during the period in income	0		0
Cash Flow Hedges [Member] | Vehicle Fuel And Other Commodity Contract [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value changes recognized during the period in other comprehensive income (losses)	195,000		(238,000)
Fair value changes recognized during the period in regulatory assets and liabilities	0		0
Pre-tax amounts reclassified into income during the period from accumulated other comprehensive income	(178,000)	[5]	3,474,000	[5]
Pre-tax amounts reclassified into income during the period from regulatory assets and liabilities	0		0
Pre-tax gains (losses) recognized during the period in income	0		0
Other Derivative Instruments [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value changes recognized during the period in other comprehensive income (losses)	0		0
Fair value changes recognized during the period in regulatory assets and liabilities	(61,756,000)		(101,427,000)
Pre-tax amounts reclassified into income during the period from accumulated other comprehensive income	0		0
Pre-tax amounts reclassified into income during the period from regulatory assets and liabilities	51,251,000		29,194,000
Pre-tax gains (losses) recognized during the period in income	6,036,000		11,139,000
Other Derivative Instruments [Member] | Electric Commodity Contract [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value changes recognized during the period in other comprehensive income (losses)	0		0
Fair value changes recognized during the period in regulatory assets and liabilities	49,818,000		3,969,000
Pre-tax amounts reclassified into income during the period from accumulated other comprehensive income	0		0
Pre-tax amounts reclassified into income during the period from regulatory assets and liabilities	(40,492,000)	[6]	(21,840,000)	[6]
Pre-tax gains (losses) recognized during the period in income	0		0
Other Derivative Instruments [Member] | Natural Gas Commodity Contract [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value changes recognized during the period in other comprehensive income (losses)	0		0
Fair value changes recognized during the period in regulatory assets and liabilities	(111,574,000)		(105,396,000)
Pre-tax amounts reclassified into income during the period from accumulated other comprehensive income	0		0
Pre-tax amounts reclassified into income during the period from regulatory assets and liabilities	91,743,000	[7]	51,034,000	[7]
Pre-tax gains (losses) recognized during the period in income	(382,000)	[8]	0
Other Derivative Instruments [Member] | Trading Commodity Contract [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value changes recognized during the period in other comprehensive income (losses)	0		0
Fair value changes recognized during the period in regulatory assets and liabilities	0		0
Pre-tax amounts reclassified into income during the period from accumulated other comprehensive income	0		0
Pre-tax amounts reclassified into income during the period from regulatory assets and liabilities	0		0
Pre-tax gains (losses) recognized during the period in income	6,418,000	[8]	11,004,000	[8]
Other Derivative Instruments [Member] | Other Contract [Member]
Impact of Derivative Activity on OCI, Regulatory Assets and Liabilities, and Income [Abstract]
Fair value changes recognized during the period in other comprehensive income (losses)			0
Fair value changes recognized during the period in regulatory assets and liabilities			0
Pre-tax amounts reclassified into income during the period from accumulated other comprehensive income			0
Pre-tax amounts reclassified into income during the period from regulatory assets and liabilities			0
Pre-tax gains (losses) recognized during the period in income			135,000	[8]
Electric Commodity [Member]
Interest Rate Derivatives [Abstract]
Notional amount	38,822,000	[10],[9]	46,794,000	[10],[9]
Natural Gas Commodity [Member]
Interest Rate Derivatives [Abstract]
Notional amount	40,736,000	[10],[9]	75,806,000	[10],[9]
Vehicle Fuel Commodity [Member]
Interest Rate Derivatives [Abstract]
Notional amount	600,000	[10],[9]	800,000	[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)
Number of months for which accumulated OCI related to interest rate derivatives are expected to be reclassified into earnings (in months)	12M
Notional amount outstanding	475,000,000
Notional amount entered into and settled	175,000,000
Mortgage-backed Securities [Member]
Changes in Level 3 Nuclear Decommissioning Fund Assets [Roll Forward]
Balance	72,589,000		81,189,000		98,461,000
Purchases	168,688,000		63,497,000		17,943,000
Settlements	(161,134,000)		(75,701,000)		(45,815,000)
Gains (losses) recognized as regulatory assets and liabilities	(1,479,000)		3,604,000		10,600,000
Balance	78,664,000		72,589,000		81,189,000
Asset-backed Securities [Member]
Changes in Level 3 Nuclear Decommissioning Fund Assets [Roll Forward]
Balance	33,174,000		11,918,000		10,962,000
Purchases	16,518,000		38,871,000		7,271,000
Settlements	(32,560,000)		(17,878,000)		(7,755,000)
Gains (losses) recognized as regulatory assets and liabilities	(631,000)		263,000		1,440,000
Balance	16,501,000		33,174,000		11,918,000
Real Estate [Member]
Changes in Level 3 Nuclear Decommissioning Fund Assets [Roll Forward]
Balance	0
Purchases	24,768,000
Settlements	0
Gains (losses) recognized as regulatory assets and liabilities	1,627,000
Balance	26,395,000
Private Equity Investments [Member]
Changes in Level 3 Nuclear Decommissioning Fund Assets [Roll Forward]
Balance	0
Purchases	9,203,000
Settlements	0
Gains (losses) recognized as regulatory assets and liabilities	0
Balance	9,203,000
Fair Value, Measurements, Recurring [Member]
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	93,000		126,000
Other derivative instruments [Abstract]
Trading commodity	19,291,000		16,154,000
Electric commodity	11,862,000		2,393,000
Natural gas commodity			376,000
Total current derivative assets	31,246,000		19,049,000
Purchased power agreements	33,094,000	[11]	35,030,000	[11]
Current derivative instruments	64,340,000		54,079,000
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	48,000		150,000
Other derivative instruments [Abstract]
Trading commodity	31,059,000		28,026,000
Natural gas commodity			977,000
Total noncurrent derivative assets	31,107,000		29,153,000
Purchased power agreements	121,780,000	[11]	154,873,000	[11]
Noncurrent derivative instruments	152,887,000		184,026,000
Derivatives designated as cash flow hedges [Abstract]
Interest rate	57,749,000
Other derivative instruments [Abstract]
Trading commodity	13,474,000		6,993,000
Electric commodity	143,000		0
Natural gas commodity	63,051,000		31,560,000
Total current derivative liabilities	134,417,000		38,553,000
Purchased power agreements	22,997,000	[11]	23,192,000	[11]
Current derivative instruments	157,414,000		61,745,000
Other derivative instruments [Abstract]
Trading commodity	15,367,000		14,282,000
Natural gas commodity			169,000
Total noncurrent derivative liabilities	15,367,000		14,451,000
Purchased power agreements	248,539,000	[11]	271,535,000	[11]
Noncurrent derivative instruments	263,906,000		285,986,000
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Nuclear decommissioning fund [Abstract]
Cash equivalents	7,103,000	[1]	76,281,000	[2]
Commingled funds	0	[1]	0	[2]
International equity funds	0	[1]	0	[2]
Private equity investments	0	[1]
Real estate	0	[1]
Debt securities [Abstract]
Government securities	0	[1]	0	[2]
U.S. corporate bonds	0	[1]	0	[2]
International corporate bonds	0	[1]	0	[2]
Municipal bonds	0	[1]	0	[2]
Asset-backed securities	0	[1]	0	[2]
Mortgage-backed securities	0	[1]	0	[2]
Equity securities [Abstract]
Common stock	398,625,000	[1]	435,270,000	[2]
Total	405,728,000	[1]	511,551,000	[2]
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	0		0
Other derivative instruments [Abstract]
Trading commodity	0		487,000
Electric commodity	0		0
Natural gas commodity			0
Total current derivative assets	0		487,000
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	0		0
Other derivative instruments [Abstract]
Trading commodity	0		0
Natural gas commodity			0
Total noncurrent derivative assets	0		0
Derivatives designated as cash flow hedges [Abstract]
Interest rate	0
Other derivative instruments [Abstract]
Trading commodity	0		392,000
Electric commodity	0		0
Natural gas commodity	418,000		20,000
Total current derivative liabilities	418,000		412,000
Other derivative instruments [Abstract]
Trading commodity	0		0
Natural gas commodity			0
Total noncurrent derivative liabilities	0		0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Nuclear decommissioning fund [Abstract]
Cash equivalents	19,020,000	[1]	7,556,000	[2]
Commingled funds	311,105,000	[1]	133,080,000	[2]
International equity funds	58,508,000	[1]	58,584,000	[2]
Private equity investments	0	[1]
Real estate	0	[1]
Debt securities [Abstract]
Government securities	117,256,000	[1]	146,654,000	[2]
U.S. corporate bonds	193,516,000	[1]	288,304,000	[2]
International corporate bonds	35,804,000	[1]	1,581,000	[2]
Municipal bonds	64,731,000	[1]	97,557,000	[2]
Asset-backed securities	0	[1]	0	[2]
Mortgage-backed securities	0	[1]	0	[2]
Equity securities [Abstract]
Common stock	0	[1]	0	[2]
Total	799,940,000	[1]	733,316,000	[2]
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	169,000		126,000
Other derivative instruments [Abstract]
Trading commodity	32,682,000		37,019,000
Electric commodity	0		0
Natural gas commodity			1,595,000
Total current derivative assets	32,851,000		38,740,000
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	107,000		150,000
Other derivative instruments [Abstract]
Trading commodity	36,599,000		32,621,000
Natural gas commodity			1,246,000
Total noncurrent derivative assets	36,706,000		34,017,000
Derivatives designated as cash flow hedges [Abstract]
Interest rate	57,749,000
Other derivative instruments [Abstract]
Trading commodity	27,891,000		30,608,000
Electric commodity	698,000		0
Natural gas commodity	70,119,000		52,709,000
Total current derivative liabilities	156,457,000		83,317,000
Other derivative instruments [Abstract]
Trading commodity	20,966,000		18,878,000
Natural gas commodity			438,000
Total noncurrent derivative liabilities	20,966,000		19,316,000
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Nuclear decommissioning fund [Abstract]
Cash equivalents	0	[1]	0	[2]
Commingled funds	0	[1]	0	[2]
International equity funds	0	[1]	0	[2]
Private equity investments	9,203,000	[1]
Real estate	26,395,000	[1]
Debt securities [Abstract]
Government securities	0	[1]	0	[2]
U.S. corporate bonds	0	[1]	0	[2]
International corporate bonds	0	[1]	0	[2]
Municipal bonds	0	[1]	0	[2]
Asset-backed securities	16,501,000	[1]	33,174,000	[2]
Mortgage-backed securities	78,664,000	[1]	72,589,000	[2]
Equity securities [Abstract]
Common stock	0	[1]	0	[2]
Total	130,763,000	[1]	105,763,000	[2]
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	0		0
Other derivative instruments [Abstract]
Trading commodity	0		0
Electric commodity	13,333,000		3,619,000
Natural gas commodity			0
Total current derivative assets	13,333,000		3,619,000
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	0		0
Other derivative instruments [Abstract]
Trading commodity	0		0
Natural gas commodity			0
Total noncurrent derivative assets	0		0
Derivatives designated as cash flow hedges [Abstract]
Interest rate	0
Other derivative instruments [Abstract]
Trading commodity	0		0
Electric commodity	916,000		1,227,000
Natural gas commodity	0		0
Total current derivative liabilities	916,000		1,227,000
Other derivative instruments [Abstract]
Trading commodity	0		0
Natural gas commodity			0
Total noncurrent derivative liabilities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value Total [Member]
Nuclear decommissioning fund [Abstract]
Cash equivalents	26,123,000	[1]	83,837,000	[2]
Commingled funds	311,105,000	[1]	133,080,000	[2]
International equity funds	58,508,000	[1]	58,584,000	[2]
Private equity investments	9,203,000	[1]
Real estate	26,395,000	[1]
Debt securities [Abstract]
Government securities	117,256,000	[1]	146,654,000	[2]
U.S. corporate bonds	193,516,000	[1]	288,304,000	[2]
International corporate bonds	35,804,000	[1]	1,581,000	[2]
Municipal bonds	64,731,000	[1]	97,557,000	[2]
Asset-backed securities	16,501,000	[1]	33,174,000	[2]
Mortgage-backed securities	78,664,000	[1]	72,589,000	[2]
Equity securities [Abstract]
Common stock	398,625,000	[1]	435,270,000	[2]
Total	1,336,431,000	[1]	1,350,630,000	[2]
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	169,000		126,000
Other derivative instruments [Abstract]
Trading commodity	32,682,000		37,506,000
Electric commodity	13,333,000		3,619,000
Natural gas commodity			1,595,000
Total current derivative assets	46,184,000		42,846,000
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	107,000		150,000
Other derivative instruments [Abstract]
Trading commodity	36,599,000		32,621,000
Natural gas commodity			1,246,000
Total noncurrent derivative assets	36,706,000		34,017,000
Derivatives designated as cash flow hedges [Abstract]
Interest rate	57,749,000
Other derivative instruments [Abstract]
Trading commodity	27,891,000		31,000,000
Electric commodity	1,614,000		1,227,000
Natural gas commodity	70,537,000		52,729,000
Total current derivative liabilities	157,791,000		84,956,000
Other derivative instruments [Abstract]
Trading commodity	20,966,000		18,878,000
Natural gas commodity			438,000
Total noncurrent derivative liabilities	20,966,000		19,316,000
Fair Value, Measurements, Recurring [Member] | Counterparty Netting [Member]
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	(76,000)	[12]	0	[12]
Other derivative instruments [Abstract]
Trading commodity	(13,391,000)	[12]	(21,352,000)	[12]
Electric commodity	(1,471,000)	[12]	(1,226,000)	[12]
Natural gas commodity			(1,219,000)	[12]
Total current derivative assets	(14,938,000)	[12]	(23,797,000)	[12]
Derivatives designated as cash flow hedges [Abstract]
Vehicle fuel and other commodity	(59,000)	[12]	0	[12]
Other derivative instruments [Abstract]
Trading commodity	(5,540,000)	[12]	(4,595,000)	[12]
Natural gas commodity			(269,000)	[12]
Total noncurrent derivative assets	(5,599,000)	[12]	(4,864,000)	[12]
Derivatives designated as cash flow hedges [Abstract]
Interest rate	0	[12]
Other derivative instruments [Abstract]
Trading commodity	(14,417,000)	[12]	(24,007,000)	[12]
Electric commodity	(1,471,000)	[12]	(1,227,000)	[12]
Natural gas commodity	(7,486,000)	[12]	(21,169,000)	[12]
Total current derivative liabilities	(23,374,000)	[12]	(46,403,000)	[12]
Other derivative instruments [Abstract]
Trading commodity	(5,599,000)	[12]	(4,596,000)	[12]
Natural gas commodity			(269,000)	[12]
Total noncurrent derivative liabilities	(5,599,000)	[12]	(4,865,000)	[12]
Cash Equivalents [Member]
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Amortized cost basis	26,123,000	[1]	83,837,000	[2]
Commingled Funds [Member]
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Amortized cost basis	320,798,000	[1]	131,000,000	[2]
International Equity Funds [Member]
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Amortized cost basis	63,781,000	[1]	54,561,000	[2]
Real Estate [Member]
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Amortized cost basis	24,768,000	[1]
Government Securities [Member]
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Amortized cost basis	116,490,000	[1]	146,473,000	[2]
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	113,179,000
Due in 1 to 5 Years	0
Due in 5 to 10 Years	4,077,000
Due after 10 Years	0
Total	117,256,000
U.S. Corporate Bonds [Member]
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Amortized cost basis	187,083,000	[1]	279,028,000	[2]
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	304,000
Due in 1 to 5 Years	35,437,000
Due in 5 to 10 Years	139,880,000
Due after 10 Years	17,895,000
Total	193,516,000
International Corporate Bonds [Member]
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Amortized cost basis	35,198,000	[1]	1,233,000	[2]
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0
Due in 1 to 5 Years	8,454,000
Due in 5 to 10 Years	23,501,000
Due after 10 Years	3,849,000
Total	35,804,000
Municipal Bonds [Member]
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Amortized cost basis	60,469,000	[1]	100,277,000	[2]
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0
Due in 1 to 5 Years	0
Due in 5 to 10 Years	40,585,000
Due after 10 Years	24,146,000
Total	64,731,000
Asset-backed Securities [Member]
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Amortized cost basis	16,516,000	[1]	32,558,000	[2]
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0
Due in 1 to 5 Years	9,907,000
Due in 5 to 10 Years	6,594,000
Due after 10 Years	0
Total	16,501,000
Mortgage-backed Securities [Member]
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Amortized cost basis	75,627,000	[1]	68,072,000	[2]
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0
Due in 1 to 5 Years	1,731,000
Due in 5 to 10 Years	1,041,000
Due after 10 Years	75,892,000
Total	78,664,000
Debt Securities [Member]
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	113,483,000
Due in 1 to 5 Years	55,529,000
Due in 5 to 10 Years	215,678,000
Due after 10 Years	121,782,000
Total	506,472,000
Common Stock [Member]
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Amortized cost basis	408,122,000	[1]	436,334,000	[2]
Private Equity Investments [Member]
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Amortized cost basis	$ 9,203,000	[1]

[1] 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.

[2] Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $97.6 million of equity investments in unconsolidated subsidiaries and $28.2 million of miscellaneous investments.

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

[4] Recorded to interest charges.

[5] Recorded to O&M expenses.

[6] 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.

[7] 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.

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

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

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

[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.