Effective Income Tax Rate Reconciliation, Change In Accounting Method, Software Development, Amount

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Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Provisional Income Tax Expense (Benefit)

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

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
Income Taxes (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Loss Carryforwards [Line Items]
Provision for income taxes	$ 106.5		$ 118.2	$ 325.4	$ 355.9
Effective tax rate (percentage)	22.10%		28.40%	22.10%	29.70%
Provision for income taxes, change in accounting method				$ 22.6
Provision for income taxes, adjustments to initial estimate impact of TCJA	$ 5.5	$ (10.3)
State and Local Jurisdiction \| Tax Year 2013 through 2016
Operating Loss Carryforwards [Line Items]
Provision for income taxes	$ (17.6)			$ 17.6