Asset Retirement Obligations - NPC - 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
Retirements	(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
NPC
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning Balance	72	74
Change in estimated costs	0	9
Retirements	(6)	(14)
Accretion	2	3
Ending Balance	68	72
Current liabilities	19	25
Other long-term liabilities	49	47
Total ARO liability	$ 68	$ 72