Significant Accounting Policies - Adoption of New Guidance Impact on Previously Reported Quarterly Results (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended																6 Months Ended	12 Months Ended
		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015	[1]	Mar. 31, 2015	[1]	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Consolidated Statement of Operations:
Operating income		$ 10		$ 66		$ 47	[1]	$ 42	[1]	$ (25)	[2]	$ 88	[2]	$ 79	[2]	$ 90	[2]		$ 166	$ 232	$ 340
Provision for income taxes																			(31)	(41)	(96)
Net income		$ 1		$ 55		$ 34	[1]	$ 29	[1]	$ 3		$ 74		$ 58		$ 63			$ 120	$ 198	$ 226
Basic EPS		$ 0.01	[3]	$ 0.38	[3]	$ 0.23	[1],[3]	$ 0.20	[1],[3]	$ 0.02	[3]	$ 0.51	[3]	$ 0.40	[3]	$ 0.44	[3]		$ 0.83	$ 1.38	$ 1.58
Diluted EPS		$ 0.01	[3]	$ 0.37	[3]	$ 0.23	[1],[3]	$ 0.20	[1],[3]	$ 0.02	[3]	$ 0.51	[3]	$ 0.40	[3]	$ 0.43	[3]		$ 0.82	$ 1.36	$ 1.55
Consolidated Statement of Cash Flows:
Net cash provided by operating activities																			$ 321	$ 418	$ 407
Net cash used in financing activities																			$ (143)	(189)	(61)
New Accounting Pronouncement, Early Adoption | ASU 2016-09
Consolidated Statement of Cash Flows:
Net cash provided by operating activities																				36	20
Net cash used in financing activities																				$ (36)	$ (20)
New Accounting Pronouncement, Early Adoption | ASU 2016-09 | As Reported
Consolidated Statement of Operations:
Operating income						$ 48		$ 42
Provision for income taxes						(11)		(11)
Net income						$ 34		$ 27
Basic EPS						$ 0.23		$ 0.19
Diluted EPS						$ 0.23		$ 0.18
Consolidated Statement of Cash Flows:
Net cash provided by operating activities								$ 120										$ 357
Net cash used in financing activities								(94)										(123)
New Accounting Pronouncement, Early Adoption | ASU 2016-09 | As Adjusted
Consolidated Statement of Operations:
Operating income	[4]					$ 47		42	[5]
Provision for income taxes	[4]					(10)		(9)	[5]
Net income	[4]					$ 34		$ 29	[5]
Basic EPS	[4]					$ 0.23		$ 0.20	[5]
Diluted EPS	[4]					$ 0.23		$ 0.20	[5]
Consolidated Statement of Cash Flows:
Net cash provided by operating activities	[5]							$ 124	[4]									363
Net cash used in financing activities	[5]							$ (98)	[4]									$ (129)

[1] In the third quarter of 2016, the Company early adopted ASU 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. Refer to “Note 2 – Significant Accounting Policies” for the impact of the adoption of this guidance on the first and second quarters of 2016.

[2] During the fourth quarter of 2015, we recognized an incremental $59 million charge over the third quarter of 2015, related to a non-cash charitable contribution recorded to general and administrative expense on our consolidated statement of operations. Refer to “Note 17 – Segments and Geographic Information” for a discussion of this charitable contribution.

[3] Earnings per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly earnings per share may not equal the total computed for the year.

[4] The election to account for forfeitures as they occur did not have a material impact for the three months ended March 31, 2016 and resulted in an increase to stock-based compensation expense of approximately $1 million for the three months ended June 30, 2016.

[5] Includes the reclassification of cash flows related to excess tax benefits from financing activities to operating activities of $4 million and $2 million for the three months ending March 31, 2016 and June 30, 2016, respectively.