Significant Accounting Policies - Components of Lease Expense (Paranthetical) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018	Dec. 31, 2017
Schedule Of Accounting Policies [Line Items]
Operating lease expense	$ 24	[1]	$ 21	$ 21
Sublease income	3	[1]	3	3
Depreciation expense	93		82	79
Interest expense	$ 7		12	15
Corporate HQ Building
Schedule Of Accounting Policies [Line Items]
Depreciation expense			3	3
Interest expense			$ 7	$ 7

[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.