Merger (Details 2) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended			10 Months Ended		12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2011 Allegheny Energy Inc		Dec. 31, 2013 Allegheny Energy Inc		Dec. 31, 2012 Allegheny Energy Inc
Revenue and earnings of Allegheny
Revenues	$ 3,647	$ 4,036	$ 3,511	$ 3,723	$ 3,493	$ 4,052	$ 3,746	$ 3,982	$ 9,479	$ 9,800	$ 10,573	$ 3,966		$ 4,331		$ 4,410
NET INCOME	$ 142	$ 218	$ (164)	$ 196	$ (148)	$ 425	$ 188	$ 306	$ 392	$ 771	$ 869	$ 147	[1]	$ (31)	[1]	$ 356	[1]
Basic earnings per share of common stock (in dollars per share)	$ 0.34	$ 0.52	$ (0.39)	$ 0.47	$ (0.35)	$ 1.02	$ 0.45	$ 0.73	$ 0.94	$ 1.85	$ 2.22	$ 0.37		$ (0.07)		$ 0.85
Diluted earnings per share of common stock (in dollars per share)	$ 0.34	$ 0.52	$ (0.39)	$ 0.47	$ (0.35)	$ 1.01	$ 0.45	$ 0.73	$ 0.94	$ 1.84	$ 2.21	$ 0.37		$ (0.07)		$ 0.85

[1] (1)Includes Allegheny’s after-tax merger costs of $58 million, $1 million and $1 million during 2011, 2012 and 2013, respectively.