Merger (Details Textuals) (USD $) In Millions, unless otherwise specified	10 Months Ended	12 Months Ended			12 Months Ended		3 Months Ended	12 Months Ended					3 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Feb. 24, 2011	Dec. 31, 2011 Allegheny Energy Inc	Feb. 24, 2011 Allegheny Energy Inc	Mar. 31, 2011 Allegheny Energy Inc Pre-tax	Dec. 31, 2012 Allegheny Energy Inc Pre-tax	Dec. 31, 2011 Allegheny Energy Inc Pre-tax	Dec. 31, 2013 Allegheny Energy Inc Pre-tax Other Operating Expense	Dec. 31, 2012 Allegheny Energy Inc Pre-tax Other Operating Expense	Dec. 31, 2011 Allegheny Energy Inc Pre-tax Other Operating Expense	Mar. 31, 2011 Allegheny Energy Inc Net of Tax	Dec. 31, 2012 Allegheny Energy Inc Net of Tax	Dec. 31, 2011 Allegheny Energy Inc Net of Tax	Dec. 31, 2013 Allegheny Energy Inc Net of Tax Other Operating Expense	Dec. 31, 2012 Allegheny Energy Inc Net of Tax Other Operating Expense	Dec. 31, 2011 Allegheny Energy Inc Net of Tax Other Operating Expense
Merger (Textuals) [Abstract]
Exchange ratio				0.667		0.667
Increase in Property Plant and Equipment Due to Business Acquisition Purchase Price Allocation					$ 4
Increase in noncurrent assets					91
Increase (Decrease) in Current Liabilities Due to Business Acquisition Purchase Price Allocation					(4)
Decrease in current assets					(16)
Decrease in goodwill					(80)
Goodwill						872
Merger transaction costs										2	1	91				1	1	73
Merger integration costs							67	6	93				42	13	91
Merger related Expenses	58	1	1
Expenses related to merger settlements approved by regulatory agencies									$ 36