Income Taxes, Provision and Effective tax rate (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Income Taxes
Provision for income taxes	$ (79.6)	$ (86.4)
Effective tax rate (as a percent)	22.80%	24.40%
Excess tax benefit from option exercises	$ 6.8	$ 4.1
Impact on provision for income taxes (in basis points)	1.90%	1.10%

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 excess tax benefit for share-based compensation cost.

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Amount of tax benefit from exercise of stock options granted under share-based compensation 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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