Quarterly Financial Information - Summary of Selected Unaudited Financial Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015	[1]	Mar. 31, 2015	[1]	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Year ended December 31, 2016
Revenue	$ 316		$ 421		$ 391		$ 352		$ 309		$ 415		$ 405		$ 363		$ 1,480	$ 1,492	$ 1,246
Operating income (loss)	10		66		47		42		(25)	[2]	88	[2]	79	[2]	90	[2]	166	232	340
Net income	$ 1		$ 55		$ 34		$ 29		$ 3		$ 74		$ 58		$ 63		$ 120	$ 198	$ 226
Basic earnings per share	$ 0.01	[3]	$ 0.38	[3]	$ 0.23	[3]	$ 0.20	[3]	$ 0.02	[3]	$ 0.51	[3]	$ 0.40	[3]	$ 0.44	[3]	$ 0.83	$ 1.38	$ 1.58
Diluted earnings per share	$ 0.01	[3]	$ 0.37	[3]	$ 0.23	[3]	$ 0.20	[3]	$ 0.02	[3]	$ 0.51	[3]	$ 0.40	[3]	$ 0.43	[3]	$ 0.82	$ 1.36	$ 1.55

[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.