Common Stock Repurchase Program (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended				9 Months Ended
	Aug. 31, 2017	Jun. 30, 2017	Feb. 28, 2017	Nov. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accelerated Share Repurchases [Line Items]
Common stock repurchases					$ 750
Cash paid for repurchase of common stock					750	$ 500
Accelerated Share Repurchase Agreement (ASR) [Member]
Accelerated Share Repurchases [Line Items]
Common stock repurchases	$ 500	$ 250		$ 225
Cash paid for repurchase of common stock	$ 500	$ 250		$ 225
Shares of common stock received under ASR	5.3	2.7	0.4	2.8
Additional share received under ASR	0.7
ASR price (dollars per share)	$ 75.25	$ 73.46		$ 63.41
ASR final weighted price (dollars per share)	$ 74.31		$ 69.43
Authorized share repurchases					$ 0