Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Tax Contingency [Line Items]
Effective tax rate	31.40%	30.50%	29.00%	31.50%
Overall increase (decrease) in unrecognized tax benefits (UTPs)	$ 122.7		$ 136.6
Expected Benefit to provision for income taxes for full-year 2017 due to change in accounting principle			$ 40.0
Expected change to tax rate for full-year 2017 due to change in accounting principle			2.25%
Excess tax benefit effect of adoption adjustment on provision for income taxes	$ 7.7		$ 35.6
Excess tax benefit effect of adoption change on provision for income taxes rates	1.60%		2.60%
Net of federal tax benefit [Member]
Income Tax Contingency [Line Items]
Overall increase (decrease) in unrecognized tax benefits (UTPs)	$ 122.6		$ 136.9
Retained Earnings [Member]
Income Tax Contingency [Line Items]
Effect of adoption adjustment Reduction to retained earnings	$ 4.6		$ 4.6