Goodwill and Other Intangibles Goodwill and Other Intangibles - (OOM - Details 3) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Apr. 02, 2014	Dec. 14, 2012
Finite-Lived Intangible Assets [Line Items]
Off-market Lease, Unfavorable	$ 1,040	$ 1,146
Accumulated Amortization of Out of Market Contracts	765	$ 664
EME [Member] | Lease Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Off-market Lease, Unfavorable			$ 159
GenOn Energy [Member] | Lease Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Off-market Lease, Unfavorable				$ 790
GenOn Energy [Member] | Gas Transportation Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Off-market Lease, Unfavorable				$ 327
Out of Market Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Future Amortization Expenses, Out-of-Market Contracts, Year One	100
Future Amortization Expenses, Out-of-Market Contracts, Year Two	95
Future Amortization Expenses, Out-of-Market Contracts, Year Three	93
Future Amortization Expenses, Out-of-Market Contracts, Year Four	93
Future Amortization Expenses, Out-of-Market Contracts, Year Five	83
Out of Market Contracts [Member] | Power Contracts
Finite-Lived Intangible Assets [Line Items]
Future Amortization Expenses, Out-of-Market Contracts, Year One	16
Future Amortization Expenses, Out-of-Market Contracts, Year Two	16
Future Amortization Expenses, Out-of-Market Contracts, Year Three	17
Future Amortization Expenses, Out-of-Market Contracts, Year Four	17
Future Amortization Expenses, Out-of-Market Contracts, Year Five	10
Out of Market Contracts [Member] | Lease Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Future Amortization Expenses, Out-of-Market Contracts, Year One	47
Future Amortization Expenses, Out-of-Market Contracts, Year Two	47
Future Amortization Expenses, Out-of-Market Contracts, Year Three	47
Future Amortization Expenses, Out-of-Market Contracts, Year Four	47
Future Amortization Expenses, Out-of-Market Contracts, Year Five	47
Out of Market Contracts [Member] | Gas Transportation Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Future Amortization Expenses, Out-of-Market Contracts, Year One	37
Future Amortization Expenses, Out-of-Market Contracts, Year Two	32
Future Amortization Expenses, Out-of-Market Contracts, Year Three	29
Future Amortization Expenses, Out-of-Market Contracts, Year Four	29
Future Amortization Expenses, Out-of-Market Contracts, Year Five	$ 26