Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2020	Dec. 31, 2019	Jul. 31, 2018	Mar. 31, 2018
Tax Credit Carryforward [Line Items]
Unrecognized tax benefits	$ 17,000,000	$ 0	$ 0	$ 0
Unrecognized tax benefits, uncertain tax positions	19,000,000
Interest and penalties expense	$ 2,000,000
Unrecognized tax benefits, net effect					$ 6,000,000
Federal
Tax Credit Carryforward [Line Items]
Operating loss carryforwards, valuation allowance		7,000,000
Operating loss carryforwards		2,600,000,000	$ 4,700,000,000
State
Tax Credit Carryforward [Line Items]
Operating loss carryforwards, valuation allowance		$ 2,000,000