Stock-Based Compensation - Summary of Stock Option Plan Activity (Detail) - Time Based and Performance Based - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options, Outstanding beginning	14,527,460	17,096,761	19,687,838
Number of Options, Granted	1,609,170	2,448,100	2,459,900
Number of Options, Forfeited	(1,808,315)	(798,279)	(383,163)
Number of Options, Exercised	(3,779,137)	(4,219,122)	(4,667,814)
Number of Options, Outstanding ending	10,549,178	14,527,460	17,096,761	19,687,838
Number of Options, Exercisable	6,111,083
Weighted-Average Exercise Price, Outstanding beginning	$ 28.80	$ 25.78	$ 22.80
Weighted-Average Exercise Price, Granted	48.24	42.01	36.65
Weighted-Average Exercise Price, Forfeited	(30.59)	(29.57)	(23.35)
Weighted-Average Exercise Price, Exercised	(21.84)	(24.08)	(19.11)
Weighted-Average Exercise Price, Outstanding ending	33.96	$ 28.80	$ 25.78	$ 22.80
Weighted-Average Exercise Price, Exercisable	$ 29.15
Weighted Average Remaining Contractual Term in Years, Outstanding Beginning	4 years 1 month 28 days	4 years 3 months 15 days	4 years 7 months 10 days	5 years 1 month 28 days
Weighted Average Remaining Contractual Term in Years, Exercisable Ending	3 years 1 month 28 days
Aggregate Intrinsic, Outstanding Beginning	$ 231	$ 344	$ 156
Aggregate Intrinsic, Outstanding Ending	136	$ 231	$ 344	$ 156
Aggregate Intrinsic, Exercisable	$ 107