Debt - Summary of Debt (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Gross Carrying Amount	$ 2,700	$ 2,700
Unamortized Discount and Deferred Financing Costs	(25)	(25)
Net Carrying Amount	2,675	2,675
Unsecured Debt | 2021 Notes
Debt Instrument [Line Items]
Gross Carrying Amount	650	650
Unamortized Discount and Deferred Financing Costs	(2)	(2)
Net Carrying Amount	648	648
Unsecured Debt | 2022 Notes
Debt Instrument [Line Items]
Gross Carrying Amount	400	400
Unamortized Discount and Deferred Financing Costs	(2)	(2)
Net Carrying Amount	398	398
Unsecured Debt | 2026 Notes
Debt Instrument [Line Items]
Gross Carrying Amount	850	850
Unamortized Discount and Deferred Financing Costs	(7)	(7)
Net Carrying Amount	843	843
Unsecured Debt | 2027 Notes
Debt Instrument [Line Items]
Gross Carrying Amount	400	400
Unamortized Discount and Deferred Financing Costs	(5)	(5)
Net Carrying Amount	395	395
Unsecured Debt | 2047 Notes
Debt Instrument [Line Items]
Gross Carrying Amount	400	400
Unamortized Discount and Deferred Financing Costs	(9)	(9)
Net Carrying Amount	$ 391	$ 391