Income Taxes - NPC - Components of Net Deferred Income Tax Liability (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities	$ 1,349	$ 1,420
Other	686	777
Total deferred income tax assets	3,159	3,178
Property-related items	(11,814)	(10,816)
Regulatory assets	(764)	(785)
Other	(478)	(327)
Total deferred income tax liabilities	(15,933)	(14,749)
Net deferred income tax liability	(12,938)	(11,775)
NPC
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities	195	206
Operating and finance leases	73	79
Customer advances	25	19
Derivative contracts and unamortized contract values	25	8
Other	8	15
Total deferred income tax assets	326	327
Property-related items	(800)	(800)
Regulatory assets	(204)	(176)
Operating and finance leases	(70)	(76)
Other	(34)	(13)
Total deferred income tax liabilities	(1,108)	(1,065)
Net deferred income tax liability	$ (782)	$ (738)