Asset Retirement Obligations - MEC - Change in Asset Retirement Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning Balance	$ 1,341	$ 1,272
Change in estimated costs	81	46
Additions	15	51
Asset Retirement Obligation, Liabilities Settled	(144)	(201)
Accretion	47	51
Ending Balance	1,340	1,341
Current liabilities	130	184
Other long-term liabilities	1,210	1,157
Total ARO liability	1,340	1,341
MEC
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning Balance	818	839
Change in estimated costs	35	47
Additions	6	23
Asset Retirement Obligation, Liabilities Settled	(103)	(124)
Accretion	31	33
Ending Balance	787	818
Current liabilities	73	109
Other long-term liabilities	714	709
Total ARO liability	787	818
Fossil fuel facilities
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning Balance	529
Ending Balance	466	529
Total ARO liability	466	529
Fossil fuel facilities | MEC
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning Balance	255
Ending Balance	161	255
Total ARO liability	$ 161	$ 255