Long-Term Investments (Equity Method Investments) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Long-Term Investments [Line Items]
Long-Term Investments		$ 896	$ 932
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%
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		$ 86	87
Power [Member] | Partnerships And Corporate Joint Ventures [Member]
Long-Term Investments [Line Items]
Long-Term Investments	[1]	86	87
Power [Member] | Partnerships And Corporate Joint Ventures [Member] | Keystone [Member]
Long-Term Investments [Line Items]
Long-Term Investments		9	8
Power [Member] | Partnerships And Corporate Joint Ventures [Member] | Conemaugh [Member]
Long-Term Investments [Line Items]
Long-Term Investments		8	8
Power [Member] | Partnerships And Corporate Joint Ventures [Member] | Kalaeloa [Member]
Long-Term Investments [Line Items]
Long-Term Investments		$ 69	$ 71

[1] During the three years ended December 31, 2018, 2017 and 2016, dividends from these investments were $16 million, $18 million and $18 million, respectively.