Income Taxes, Provision and Effective tax rate (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Taxes
Provision for income taxes	$ (78.7)	$ (94.5)	$ (158.3)	$ (180.9)
Effective tax rate (as a percent)	21.30%	24.70%	22.00%	24.50%
Excess tax benefit from option exercises	$ 12.9	$ 3.0	$ 19.7	$ 7.1
Impact of provision for income taxes (in basis points)	(3.50%)	(0.80%)	(2.70%)	(1.00%)

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to expense for award under share-based payment arrangement. Excludes expense determined to be nondeductible upon grant or after for award under share-based payment arrangement.

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Amount of tax benefit from exercise of option under share-based payment arrangement.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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