Regulatory Matters - NPC - Regulatory Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Regulatory Liabilities [Line Items]
Total regulatory liabilities	$ 7,214	$ 7,475
Regulatory liabilities	254	254
Regulatory liabilities	$ 6,960	7,221
Cost of removal
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	26 years
Total regulatory liabilities	$ 2,424	2,435
Other
Regulatory Liabilities [Line Items]
Total regulatory liabilities	758	667
NPC
Regulatory Liabilities [Line Items]
Total regulatory liabilities	1,149	1,213
Regulatory liabilities	49	50
Regulatory liabilities	1,100	1,163
NPC | Deferred income taxes
Regulatory Liabilities [Line Items]
Total regulatory liabilities	$ 603	647
NPC | Cost of removal
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	31 years
Total regulatory liabilities	$ 348	340
NPC | Other
Regulatory Liabilities [Line Items]
Total regulatory liabilities	$ 198	$ 226