Effect of New Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax benefit recognized	$ (41.1)	$ (35.5)	$ (90.0)	$ (55.9)
Reclassification of payments from investing activities to operating activities			459.1	368.9
Reclassification of payments from investing activities to financing activities			$ (46.6)	(10.1)
Description of contracts renewal period			One year or less
Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of payments from investing activities to operating activities				19.5
Reclassification of payments from investing activities to financing activities				41.7
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax benefit recognized	$ 1.8	$ 1.7	$ 11.9	$ 4.8