Income Taxes, 2017 Tax Cuts and Jobs Act (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017 USD ($) item	Dec. 31, 2017
Income Taxes
U.S. statutory federal tax rate (as a percent)	21.00%		35.00%
Estimated Tax Act Charge		$ 398.5
Estimated Transition Tax		259.4
Provisional charge on unremitted foreign earnings		176.6
Income tax expense (benefit) associated with the remeasurement of net deferred tax liabilities		$ (37.5)
Number of components | item		3