Capital Stock, Dividends and Share Repurchases - Stock Repurchase Programs (Parenthetical) (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended
	Feb. 28, 2015	Jul. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock Repurchase Program [Line Items]
Cash paid for repurchase of common stock			$ 600	$ 600	$ 239
Initial shares of common stock received under ASR			14,823,000	9,569,000	5,368,000
Accelerated Share Repurchase Agreement (ASR) [Member]
Stock Repurchase Program [Line Items]
Accelerated share repurchase percentage of shares expected to be repurchased			70.00%	70.00%
Cash paid for repurchase of common stock		$ 600
Common stock repurchases		$ 600
Initial shares of common stock received under ASR		9,600,000
Accelerated share repurchase,price per share		$ 43.89
Shares received from the banks to settle the ASRs	2,800,000
Accelerated Share Repurchase Agreement (ASR) [Member] | Weighted Average [Member]
Stock Repurchase Program [Line Items]
Accelerated share repurchase,price per share	$ 48.58