Income Taxes - Components of Net Deferred Income Tax Liability (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred income tax assets: [Abstract]
Federal, state and foreign carryforwards	$ 677	$ 575
Regulatory liabilities	1,420	1,610
AROs	304	306
Other	777	590
Total deferred income tax assets	3,178	3,081
Valuation allowances	(204)	(143)
Total deferred income tax assets, net	2,974	2,938
Deferred income tax liabilities: [ Abstract]
Property-related items	(10,816)	(10,439)
Regulatory assets	(785)	(631)
Investments	(2,821)	(1,137)
Other	(327)	(384)
Total deferred income tax liabilities	(14,749)	(12,591)
Net deferred income tax liability	$ (11,775)	$ (9,653)