Summary of Significant Accounting Policies, Regulated Operations (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Schedule of Regulatory Assets and Liabilities [Line Items]
Fuel clause under recoveries	$ 1.8		$ 1.0
Regulatory Assets, Current	16.0		5.9
Regulatory Assets, Non - Current	507.9		489.4
Regulatory Liability, Current	45.7		50.8
Deferred Fuel Cost Current Liabilities	7.7		29.9
Regulatory Liability, Non - Current	230.7		193.1
Smart Grid rider over collections [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	24.3		10.4
Other [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	13.7	[1]	10.5	[1]
Accrued removal obligations, net [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Non - Current	208.2	[1],[2]	184.9
Pension tracker [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Non - Current	22.5		8.2
Other [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	14.2	[2]	4.9	[2]
Regulatory Assets, Non - Current	10.4		9.0
Benefit obligations regulatory asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Non - Current	359.2		365.5
Income taxes recoverable from customers, net [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Non - Current	54.0		43.3
Smart Grid [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Non - Current	37.2		14.2
Deferred storm expenses [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Non - Current	23.8		28.6
Unamortized loss on reacquired debt [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Non - Current	14.2		15.3
Deferred Pension Plan expenses [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Non - Current	$ 9.1		$ 13.5

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

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