Income Taxes - Schedule of Current and Deferred Taxes Charged to (Benefit) Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current
Federal	$ 11	$ 17	$ (20)
State	(6)	2	12
Current taxes charged to expense (benefit)	5	19	(8)
Deferred
Federal	152	233	(124)
State	44	(12)	(73)
Deferred taxes charged to expense (benefit)	196	221	(197)
Production tax credits	(57)	(68)	(53)
Investment tax credits	(1)	(2)	(1)
Total Income Tax Expense (Benefit)	$ 143	$ 170	$ (259)