Other Comprehensive Income - Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Comprehensive Income Loss [Line Items]
Total other comprehensive income, Gross		$ 1	$ 1	$ 6
Total other comprehensive income, Tax		0	0	(2)
Total other comprehensive income, net of tax		1	1	4
Net unrealized losses from cash flow hedges	[1]	(2)	(3)
Total accumulated other comprehensive loss		(2)	(3)
Accumulated Gain on Cash Flow Hedges [Member]
Other Comprehensive Income Loss [Line Items]
Unrealized gain on cash flow hedges, Gross		0	0	4
Reclassification from AOCI to net income, Gross		1	1	2
Total other comprehensive income, Gross		1	1	6
Unrealized gain on cash flow hedges, Tax		0	0	(1)
Reclassification from AOCI to net income, Tax		0	0	(1)
Total other comprehensive income, Tax		0	0	(2)
Unrealized gain on cash flow hedges, Net		0	0	3
Reclassification from AOCI to net income, Net		1	1	1
Total other comprehensive income, net of tax		$ 1	$ 1	$ 4

[1] Net of tax benefit of $1 million and $2 million as of December 31, 2017 and 2016, respectively.