Income Taxes - Income tax changes (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Dec. 22, 2017	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2008	Dec. 31, 2007
Income Taxes
Corporate tax rate (as a percent)	35.00%		21.00%	21.00%	35.00%
U.S. federal and state tax liability related to transition tax on repatriation of foreign earnings and profits			$ 52.2
Amount of deemed repatriation of foreign earnings and profits			946.0
Income tax benefit related to remeasurement of deferred tax assets and liabilities due to change in enacted tax rate			301.2
Adjustments to provisional estimates :
Federal and State Change Due to Repatriation		$ 12.5
Other Adjustments		(0.9)
Total SAB 118 Benefit		$ 11.6
Provisional estimate, income tax benefit from enactment of the Act			243.4
Income tax benefit from enactment of the Act			$ 255.0