Segment Information (Details Textuals) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012		Sep. 30, 2012
Segment Reporting Information [Line Items]
Reportable Operating Segments			3
Number of existing utility operating companies			10
Regulated Distribution
Segment Reporting Information [Line Items]
Number of customers served by utility operating companies			6,000,000
Number of square miles in service area	65,000		65,000
Regulated Distribution | Net Income | Previously Expensing Costs to be Capitalized
Segment Reporting Information [Line Items]
Error correction, corrected in current period	$ 21.8	[1]	$ 15.1	[1]
Competitive Energy Services
Segment Reporting Information [Line Items]
Megawatts of net demonstrated capacity of competitive segment	17,000		17,000
Competitive Energy Services | Unregulated Plants Expected to be Closed by 9/1/2012
Segment Reporting Information [Line Items]
Megawatt capacity of plants expected to be closed	2,700		2,700

[1] Regulated Distribution net income for the three and nine months ended September 30, 2012, include adjustments of $21.8 million and $15.1 million, respectively, from capitalizing various construction activities of the Allegheny Utilities that were previously expensed. The effect of these adjustments was not material to the current or previous periods.