Significant Accounting Policies - Future Minimum Commitments Under Our corporate Headquarters Lease and Other Non-Cancelable Operating Leases (Details) $ in Millions	Dec. 31, 2018 USD ($)
Schedule Of Accounting Policies [Line Items]
2019	$ (3)
2020	(2)
2021	(2)
2022	(2)
Total	(9)
2019	25
2020	25
2021	24
2022	24
2023	19
Thereafter	76
Total	193
Headquarters Lease
Schedule Of Accounting Policies [Line Items]
2019	9	[1]
2020	9	[1]
2021	10	[1]
2022	10	[1]
2023	10	[1]
Thereafter	67	[1]
Total	115	[1]
Other Operating Leases
Schedule Of Accounting Policies [Line Items]
2019	19
2020	18
2021	16
2022	16
2023	9
Thereafter	9
Total	$ 87

[1] Amount includes an $83 million financing obligation in other long-term liabilities on our consolidated balance sheet at December 31, 2018, related to the Headquarters Lease.