Share-Based Compensation - Stock Option Activity Table (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward]
Shares exercised	(1.31)	(1.00)	(2.00)
Stock Option [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward]
Shares outstanding at January 1, 2012	9.87
Shares granted	0.88
Shares exercised	(1.31)
Shares forfeited or expired	(0.08)
Shares outstanding at December 31, 2012	9.36
Shares vested or expected to vest at December 31, 2012	9.26
Shares exercisable at December 31, 2012	6.78
Weighted-average exercise price, outstanding at January 1, 2012	55.27
Granted weighted-average exercise price	70.33
Exercised weighted-average exercise price	40.04
Forfeited or expired weighted-average exercise price	72.23
Weighted-average exercise price, outstanding at December 31, 2012	58.66
Weighted-average exercise price, vested or expected to vest at December 31, 2012	58.50
Weighted-average exercise price, exercisable at December 31, 2012	52.59
Weighted-average remaining contractual term, outstanding at December 31, 2012	3 years 11 months 1 day
Weighted-average remaining contractual term, vested or expected to vest at December 31, 2012	3 years 10 months 24 days
Weighted-average remaining contractual term, exercisable at December 31, 2012	3 years 3 months 5 days
Aggregate intrinsic value, outstanding at December 31, 2012	158.6
Aggregate intrinsic value, vested or expected to vest at December 31, 2012	158.3
Aggregate intrinsic value, exercisable at December 31, 2012	151.4