Common Stock Repurchase Program - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions	1 Months Ended			6 Months Ended
	Jun. 30, 2017	Feb. 28, 2017	Nov. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Stock Repurchase Program [Line Items]
Common stock repurchases				$ 250,000,000
Cash paid for repurchase of common stock				250,000,000	$ 500,000,000
Maximum capital allocated for repurchases of shares	$ 500,000,000			$ 500,000,000
Accelerated Share Repurchase Agreement (ASR) [Member]
Stock Repurchase Program [Line Items]
Common stock repurchases	$ 250,000,000		$ 225,000,000
Shares of common stock received under ASR	2.7	0.4	2.8
Cash paid for repurchase of common stock	$ 250,000,000		$ 225,000,000
Accelerated share repurchase, price per share	$ 73.46		$ 63.41	$ 73.46
Accelerated Share Repurchase Agreement (ASR) [Member] | Weighted Average [Member]
Stock Repurchase Program [Line Items]
Final weighted average per share purchase price during the repurchase period		$ 69.43