Income Taxes - NPC - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Components of Income Tax Expense (Benefit) [Line Items]
Current	$ (1,778)	$ (1,572)	$ (888)
Deferred	650	1,883	296
Investment tax credits	(4)	(3)	(6)
Total	(1,132)	308	(598)
NPC
Components of Income Tax Expense (Benefit) [Line Items]
Current	37	57	105
Deferred	0	(10)	(31)
Investment tax credits	0	0	(1)
Total	$ 37	$ 47	$ 73