Significant Accounting Policies - Components of Lease Expense (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018	Dec. 31, 2017
Lease Cost [Abstract]
Operating lease cost		$ 24	[1]	$ 21	$ 21
Finance lease cost
Amortization of right-of-use assets	[2]	9
Interest on lease liabilities	[3]	4
Total finance lease cost		13
Sublease income		(3)	[1]	$ (3)	$ (3)
Total lease cost, net		$ 34

[1] Operating lease costs, net of sublease income, are included within operating expenses in our consolidated statement of operations. During both the years ended December 31, 2018 and 2017, we recorded operating lease expense of $21 million and sublease income of $3 million, in our consolidated statement of operations in accordance with ASC 840.

[2] Amount is included in depreciation expense in our consolidated statement of operations. During both the years ended December 31, 2018 and 2017, we recorded depreciation expense of $3 million related to our Headquarters Lease in our consolidated statement of operations in accordance with ASC 840.

[3] Amount is included in interest expense in our consolidated statement of operations. During both the years ended December 31, 2018 and 2017, we recorded interest expense of $7 million related to our Headquarters Lease in our consolidated statement of operations in accordance with ASC 840.