Common Stock Repurchase Program (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended		3 Months Ended
	Mar. 31, 2018	Feb. 28, 2018	Mar. 31, 2018	Dec. 31, 2017
Accelerated Share Repurchases [Line Items]
Common stock repurchases			$ 258
Cash paid for repurchase of common stock			250
Accrued liabilities	$ 1,031		1,031	$ 980
Authorized share repurchases	$ 992		992
Accelerated Share Repurchase Agreement (ASR) [Member]
Accelerated Share Repurchases [Line Items]
Common stock repurchases		$ 250
Cash paid for repurchase of common stock		$ 250
Shares repurchased	0.6	2.3
ASR price (dollars per share)		$ 85.13
Weighted average per share purchase price	$ 85.15
10b5-1 Plan [Member]
Accelerated Share Repurchases [Line Items]
Shares repurchased	0.1
Accrued liabilities	$ 8		$ 8