Guarantees (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Guarantor Obligations
Under 1 Year	$ 1,138
1-3 Years	188
3-5 Years	257
Over 5 Years	1,184
Guarantees by Remaining Maturity, Total	2,767	$ 1,960
Letters of credit and surety bonds
Guarantor Obligations
Under 1 Year	1,138
1-3 Years	79
3-5 Years	0
Over 5 Years	36
Guarantees by Remaining Maturity, Total	$ 1,253	1,003
Letters of credit and surety bonds, maximum expiration period (in years)	1 year
Asset sales guarantee obligations
Guarantor Obligations
Under 1 Year	$ 0
1-3 Years	4
3-5 Years	257
Over 5 Years	532
Guarantees by Remaining Maturity, Total	793	312
Other guarantees
Guarantor Obligations
Under 1 Year	0
1-3 Years	105
3-5 Years	0
Over 5 Years	616
Guarantees by Remaining Maturity, Total	721	645
Eliminations | Letters of credit and surety bonds
Guarantor Obligations
Guarantees by Remaining Maturity, Total		$ 92
GenOn | Letters of credit and surety bonds
Guarantor Obligations
Guarantees by Remaining Maturity, Total	$ 32