Long-Term Investments (Equity Method Investments) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Long-Term Investments [Line Items]
Long-Term Investments		$ 1,233	$ 1,307
Keystone [Member]
Long-Term Investments [Line Items]
Location of the affiliated companies, equity method investments		PA
Owned percentage		23.00%
Conemaugh [Member]
Long-Term Investments [Line Items]
Location of the affiliated companies, equity method investments		PA
Owned percentage		23.00%
PennEast [Member]
Long-Term Investments [Line Items]
Location of the affiliated companies, equity method investments		PA
Owned percentage		12.00%
Kalaeloa [Member]
Long-Term Investments [Line Items]
Location of the affiliated companies, equity method investments		HI
Owned percentage		50.00%
Power [Member]
Long-Term Investments [Line Items]
Long-Term Investments		$ 119	121
Power [Member] | Partnerships And Corporate Joint Ventures [Member]
Long-Term Investments [Line Items]
Long-Term Investments	[1]	119	$ 121
Power [Member] | Partnerships And Corporate Joint Ventures [Member] | Keystone [Member]
Long-Term Investments [Line Items]
Long-Term Investments		0
Power [Member] | Partnerships And Corporate Joint Ventures [Member] | Conemaugh [Member]
Long-Term Investments [Line Items]
Long-Term Investments		0
Power [Member] | Partnerships And Corporate Joint Ventures [Member] | PennEast [Member]
Long-Term Investments [Line Items]
Long-Term Investments		0
Power [Member] | Partnerships And Corporate Joint Ventures [Member] | Kalaeloa [Member]
Long-Term Investments [Line Items]
Long-Term Investments		$ 0

[1] During the three years ended December 31, 2015, 2014 and 2013, the amount of dividends from these investments was $16 million, $17 million and $11 million, respectively.