Common Stock Repurchase Program (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended		3 Months Ended			6 Months Ended
	May 31, 2019	Jan. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Accelerated Share Repurchases [Line Items]
Total repurchases			$ 180		$ 292	$ 244	$ 550
Authorized share repurchases			$ 1,300			1,300		$ 1,500	$ 1,250
Cash paid for repurchase of common stock						$ 248	$ 550
10b5-1 Plan [Member]
Accelerated Share Repurchases [Line Items]
Shares repurchased				0.7
Total repurchases				$ 64
Weighted average per share purchase price				$ 94.35
Cash paid for repurchase of common stock		$ 4
Accelerated Share Repurchase Agreement (ASR) [Member]
Accelerated Share Repurchases [Line Items]
Authorized share repurchases	$ 180
Cash paid for repurchase of common stock	$ 180
Shares received (in shares)	1.3
Stock price (in dollars per share)	$ 109.59