Income Taxes Tax Cut and Jobs Act (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018
Income Tax Contingency [Line Items]
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)	$ 87.0	$ (4.8)
Remeasurement Tax [Domain]
Income Tax Contingency [Line Items]
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)	75.0	(5.1)
Toll Tax [Domain]
Income Tax Contingency [Line Items]
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)	8.0	0.7
Assertion Tax [Domain]
Income Tax Contingency [Line Items]
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)	$ 4.0	$ (0.4)