Income Taxes, Provision and Effective tax rate (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Taxes
Provision for income taxes	$ (100.0)	$ (78.1)	$ (280.8)	$ (212.7)
Effective tax rate (as a percent)	23.80%	21.80%	24.30%	21.80%
Excess tax benefit from option exercises	$ 7.0	$ 16.6	$ 14.1	$ 45.8
Impact on provision for income taxes (in basis points)	1.70%	4.70%	1.20%	4.70%