Summary of Significant Accounting Policies, Regulated Operations (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	$ 41.9		$ 5.9
Regulatory Assets, Non - Current	415.3		489.4
Regulatory Liability, Current	47.7		50.8
Regulatory Liability, Non - Current	223.2		193.1
Fuel clause under recoveries [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	33.2		1.0
Benefit obligations regulatory asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Non - Current	274.0		365.5
Income taxes recoverable from customers, net [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Non - Current	51.8		43.3
Smart Grid [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Non - Current	29.4		14.2
Deferred storm expenses [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Non - Current	25.5		28.6
Unamortized loss on reacquired debt [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Non - Current	14.5		15.3
Deferred Pension Plan expenses [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Non - Current	10.2		13.5
Red Rock deferred expenses [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Non - Current	6.9		7.2
Other [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	8.7	[1]	4.9	[1]
Regulatory Assets, Non - Current	3.0		1.8
Smart Grid rider over collections [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	23.5		10.4
Fuel clause over recoveries [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	8.5		29.9
Accrued removal obligations, net [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Non - Current	204.5		184.9
Pension tracker [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Non - Current	18.7		8.2
Other [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	$ 15.7	[2]	$ 10.5	[2]

[1] Included in Other Current Assets on the Condensed Consolidated Balance Sheets.

[2] Included in Other Current Liabilities on the Condensed Consolidated Balance Sheets.