Debt - Summary of Debt (Details) - USD ($) $ in Millions	Dec. 31, 2017	May 26, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Gross Carrying Amount	$ 4,440		$ 4,940
Unamortized Discount and Deferred Financing Costs	(50)		(53)
Net Carrying Amount	4,390		4,887
Credit Facilities | 2017 TLA
Debt Instrument [Line Items]
Gross Carrying Amount	990
Unamortized Discount and Deferred Financing Costs	(8)
Net Carrying Amount	982
Credit Facilities | 2016 TLA
Debt Instrument [Line Items]
Gross Carrying Amount			2,690
Unamortized Discount and Deferred Financing Costs			(27)
Net Carrying Amount			2,663
Unsecured Notes | 2021 Notes
Debt Instrument [Line Items]
Gross Carrying Amount	650		650
Unamortized Discount and Deferred Financing Costs	(4)		(5)
Net Carrying Amount	646		645
Unsecured Notes | 2022 Notes
Debt Instrument [Line Items]
Gross Carrying Amount	400	$ 400
Unamortized Discount and Deferred Financing Costs	(4)
Net Carrying Amount	396
Unsecured Notes | 2023 Notes
Debt Instrument [Line Items]
Gross Carrying Amount	750		750
Unamortized Discount and Deferred Financing Costs	(9)		(11)
Net Carrying Amount	741		739
Unsecured Notes | 2026 Notes
Debt Instrument [Line Items]
Gross Carrying Amount	850		850
Unamortized Discount and Deferred Financing Costs	(9)		(10)
Net Carrying Amount	841		$ 840
Unsecured Notes | 2027 Notes
Debt Instrument [Line Items]
Gross Carrying Amount	400	400
Unamortized Discount and Deferred Financing Costs	(6)
Net Carrying Amount	394
Unsecured Notes | 2047 Notes
Debt Instrument [Line Items]
Gross Carrying Amount	400	$ 400
Unamortized Discount and Deferred Financing Costs	(10)
Net Carrying Amount	$ 390