Common Stock Repurchase Program (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2019	May 31, 2019	Jan. 31, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Accelerated Share Repurchases [Line Items]
Cash paid for repurchase of common stock						$ 248	$ 750
Total repurchases					$ 200	244	$ 750
Authorized share repurchases	$ 1,300					$ 1,300		$ 1,500	$ 1,250
10b5-1 Plan [Member]
Accelerated Share Repurchases [Line Items]
Cash paid for repurchase of common stock			$ 4
Shares repurchased (in shares)				0.7
Total repurchases				$ 64
Weighted average per share purchase price				$ 94.35
Accelerated Share Repurchase Agreement (ASR) [Member]
Accelerated Share Repurchases [Line Items]
Cash paid for repurchase of common stock		$ 180
Shares repurchased (in shares)	0.3	1.3
Weighted average per share purchase price	$ 114.76
Authorized share repurchases		$ 180
Stock price (in dollars per share)		$ 109.59