Share-Based Compensation - Stock Option Activity Table (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward]
Shares outstanding at January 1, 2014	7.72
Shares granted	0.95
Shares exercised	(1.85)	[1]	(2.00)	(1.00)
Shares forfeited or expired	(0.03)
Shares outstanding at December 31, 2014	6.79		7.72
Shares vested or expected to vest at December 31, 2014	6.73
Shares exercisable at December 31, 2014	4.99
Weighted-average exercise price, outstanding at January 1, 2014	$ 63.30
Granted weighted-average exercise price	$ 93.34
Exercised weighted-average exercise price	$ 54.03	[1]
Forfeited or expired weighted-average exercise price	$ 76.00
Weighted-average exercise price, outstanding at December 31, 2014	$ 69.96		$ 63.30
Weighted-average exercise price, vested or expected to vest at December 31, 2014	$ 69.79
Weighted-average exercise price, exercisable at December 31, 2014	$ 62.91
Weighted-average remaining contractual term, outstanding at December 31, 2014	3 years 6 months 22 days
Weighted-average remaining contractual term, vested or expected to vest at December 31, 2014	3 years 6 months 15 days
Weighted-average remaining contractual term, exercisable at December 31, 2014	2 years 7 months 6 days
Aggregate intrinsic value, outstanding at December 31, 2014	$ 104.3
Aggregate intrinsic value, vested or expected to vest at December 31, 2014	104.2
Aggregate intrinsic value, exercisable at December 31, 2014	101.1
Total intrinsic value of stock options exercised during the period	$ 88		$ 80	$ 49

[1] The total intrinsic value of stock options exercised was $88 million during 2014, $80 million during 2013, and $49 million during 2012, based on the difference between the market price at the exercise date and the exercise price.