Long-Term Investments (Equity Method Investments) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Long-Term Investments [Line Items]
Long-Term Investments		$ 1,050	$ 1,233
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		10.00%
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		$ 102	119
Power [Member] | Partnerships And Corporate Joint Ventures [Member]
Long-Term Investments [Line Items]
Long-Term Investments	[1]	102	119
Power [Member] | Partnerships And Corporate Joint Ventures [Member] | Keystone [Member]
Long-Term Investments [Line Items]
Long-Term Investments		7	16
Power [Member] | Partnerships And Corporate Joint Ventures [Member] | Conemaugh [Member]
Long-Term Investments [Line Items]
Long-Term Investments		8	14
Power [Member] | Partnerships And Corporate Joint Ventures [Member] | PennEast [Member]
Long-Term Investments [Line Items]
Long-Term Investments		11	5
Power [Member] | Partnerships And Corporate Joint Ventures [Member] | Kalaeloa [Member]
Long-Term Investments [Line Items]
Long-Term Investments		$ 76	$ 84

[1] During the three years ended December 31, 2016, 2015 and 2014, dividends from these investments were $18 million, $16 million and $17 million, respectively.