Business Segments - Summary of Operating Results by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue:
Total revenue	$ 777	$ 651	$ 1,541	$ 1,282
Operating profit (loss):
Total operating loss	$ 18	$ (14)	$ 25	$ (35)
Operating profit (loss) % of revenue:
Total operating loss %	2.30%	(2.20%)	1.60%	(2.70%)
United States [Member]
Revenue:
Total revenue	$ 600	$ 481	$ 1,162	$ 920
Operating profit (loss):
Total operating loss	$ 16	$ (16)	$ 19	$ (42)
Operating profit (loss) % of revenue:
Total operating loss %	2.70%	(3.30%)	1.60%	(4.60%)
Canada [Member]
Revenue:
Total revenue	$ 75	$ 79	$ 177	$ 175
Operating profit (loss):
Total operating loss	$ 1	$ 2	$ 5	$ 5
Operating profit (loss) % of revenue:
Total operating loss %	1.30%	2.50%	2.80%	2.90%
International [Member]
Revenue:
Total revenue	$ 102	$ 91	$ 202	$ 187
Operating profit (loss):
Total operating loss	$ 1		$ 1	$ 2
Operating profit (loss) % of revenue:
Total operating loss %	1.00%	0.00%	0.50%	1.10%