Significant Accounting Policies - Summary of Changes in the Allowance for Doubtful Accounts (Detail) (Allowance for Doubtful Accounts, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowance for Doubtful Accounts
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance, beginning of period	$ 3	$ 3	$ 5
Charges (recoveries) to earnings	3	1	(1)
Write-offs, net of recoveries and other adjustments	1	(1)	(1)
Balance, end of period	$ 7	$ 3	$ 3