Stockholder's Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Oct. 21, 2015	Jul. 22, 2015
Stockholders' Equity [Line Items]
Shares issued in equity offering		18,400,000
Price per share received in equity offering		$ 54.50
Proceeds from issuance of common stock, net		$ 971
Subsequent Event
Stockholders' Equity [Line Items]
Shares issued in equity offering	10,000,000
Price per share received in equity offering	$ 49.00
Proceeds from issuance of common stock, net	$ 477
Subsequent Event | Over-Allotment Option | Maximum
Stockholders' Equity [Line Items]
Shares issued in equity offering	1,500,000