Significant Accounting Policies - Adoption of ASC 842 on Unaudited Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Millions		Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
ASSETS
Prepaid expenses and other current assets		$ 35		$ 33
Property and equipment, net		262		253	[1]
Operating lease right-of-use assets		75
Deferred income taxes, net				27
Other long-term assets		101		98
Liabilities:
Accrued expenses and other current liabilities		181		151	[2]
Other long-term liabilities		341		282	[1]
Retained earnings		$ 1,106		$ 1,043	[3]
Accounting Standards Update 2016-02
ASSETS
Prepaid expenses and other current assets			$ 30
Property and equipment, net	[1]		261
Operating lease right-of-use assets	[1]		75
Deferred income taxes, net			26
Other long-term assets			96
Liabilities:
Accrued expenses and other current liabilities	[2]		172
Other long-term liabilities	[1]		335
Retained earnings	[3]		1,046
Accounting Standards Update 2016-02 | Adjustments Due to ASC 842
ASSETS
Prepaid expenses and other current assets			(3)
Property and equipment, net	[1]		8
Operating lease right-of-use assets	[1]		75
Deferred income taxes, net			(1)
Other long-term assets			(2)
Liabilities:
Accrued expenses and other current liabilities	[2]		21
Other long-term liabilities	[1]		53
Retained earnings	[3]		$ 3

[1] Refer to the below discussion regarding the transition accounting for operating and finance leases upon adoption of ASC 842.

[2] This adjustment primarily represents the short-term portion of operating and finance lease obligations recorded upon adoption of ASC 842, discussed below.

[3] Represents a cumulative-effect adjustment of $3 million, net of tax to our beginning balance of retained earnings recorded upon adoption of ASC 842.