Common Stock Repurchase Program - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		1 Months Ended						9 Months Ended
	Aug. 31, 2016	May 31, 2016	Apr. 30, 2016	Mar. 31, 2016	Feb. 29, 2016	Jan. 31, 2016	Dec. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Accelerated Share Repurchases [Line Items]
Common stock repurchases								$ 500
Cash paid for repurchase of common stock								500	$ 600
Authorization of future share repurchase								$ 650
Accelerated Share Repurchase Agreement (ASR) [Member]
Accelerated Share Repurchases [Line Items]
Common stock repurchases		$ 250		$ 100			$ 150
Shares of common stock received under ASR	0.5	3.3	0.5	1.2	0.9	2.0
Cash paid for repurchase of common stock		$ 250		$ 100		$ 150
Accelerated share repurchase, price per share		$ 60.49		$ 56.95		$ 53.37
Accelerated Share Repurchase Agreement (ASR) [Member] | Weighted Average [Member]
Accelerated Share Repurchases [Line Items]
Final weighted average per share purchase price during the repurchase period	$ 64.67		$ 58.33		$ 53.15