Business Segments - Summary of Operating Results by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Revenue:
Total revenue	$ 753	$ 1,070	$ 2,366	$ 3,099
Operating profit (loss):
Total operating profit (loss)	$ (291)	$ 50	$ (326)	$ 155
Operating profit (loss) % of revenue:
Total operating profit (loss) %	(38.60%)	4.70%	(13.80%)	5.00%
United States [Member]
Revenue:
Total revenue	$ 497	$ 748	$ 1,594	$ 2,114
Operating profit (loss):
Total operating profit (loss)	$ (294)	$ 28	$ (329)	$ 86
Operating profit (loss) % of revenue:
Total operating profit (loss) %	(59.20%)	3.70%	(20.60%)	4.10%
Canada [Member]
Revenue:
Total revenue	$ 94	$ 173	$ 299	$ 489
Operating profit (loss):
Total operating profit (loss)	$ 2	$ 14		$ 33
Operating profit (loss) % of revenue:
Total operating profit (loss) %	2.10%	8.10%	0.00%	6.70%
International [Member]
Revenue:
Total revenue	$ 162	$ 149	$ 473	$ 496
Operating profit (loss):
Total operating profit (loss)	$ 1	$ 8	$ 3	$ 36
Operating profit (loss) % of revenue:
Total operating profit (loss) %	0.60%	5.40%	0.60%	7.30%