Income Taxes - Components of Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current tax benefit (expense)
Federal	$ 24	$ 39	$ 0
State	(70)	(63)	(28)
Puerto Rico	2	(25)	(1)
Total current tax expense	(44)	(49)	(29)
Deferred tax benefit (expense)
Federal	(954)	(750)	1,182
State	(125)	(160)	173
Puerto Rico	(12)	(70)	49
Total deferred tax (expense) benefit	(1,091)	(980)	1,404
Total income tax (expense) benefit	$ (1,135)	$ (1,029)	$ 1,375