Stock Option Plans - Stock Option Activity and Related Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares Under Option, Beginning balance	10.3	8.8	8.4
Shares Under Option, Granted	1.7	2.6	1.9
Shares Under Option, Exercised	(1.3)	(1.1)	(1.4)
Shares Under Option, Forfeited or canceled	(0.1)		(0.1)
Shares Under Option, Ending balance	10.6	10.3	8.8
Shares Under Option, Exercisable at end of year	2.5	2.2	2.1
Shares Under Option, Ending vested and expected to vest	10.4	10.1	8.7
Weighted Average Exercise Price, Beginning balance	$ 41.40	$ 39.25	$ 35.49
Weighted Average Exercise Price, Granted	56.87	43.72	46.19
Weighted Average Exercise Price, Exercised	33.11	29.50	27.59
Weighted Average Exercise Price, Forfeited or canceled	34.33		27.59
Weighted Average Exercised Price, Ending balance	44.95	41.40	39.25
Weighted Average Exercise Price, Exercisable at end of year	37.81	32.37	28.54
Weighted Average Exercise price, Ending vested and expected to vest	$ 44.88	$ 41.34	$ 39.15
Weighted Average Remaining Contractual Term (in years), Ending balance	3 years 11 months 8 days	4 years 1 month 24 days	4 years 1 month 27 days
Weighted Average Remaining Contractual Term (in years), Exercisable at end of year	1 year 8 months 26 days	1 year 8 months 23 days	1 year 11 months 1 day
Weighted Average Remaining Contractual Term (in years), Ending vested and expected to vest	3 years 11 months 1 day	4 years 1 month 13 days	4 years 1 month 16 days
Aggregate Intrinsic Value, Ending Balance	$ 193.4	$ 108.8	$ 36.7
Aggregate Intrinsic Value, Exercisable at end of year	64.0	43.7	25.9
Aggregate Intrinsic Value, Ending vested and expected to vest	$ 191.1	$ 107.5	$ 36.6