Goodwill and Identifiable Assets (Future Amortization Expense) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Net Carrying Amount	$ 216.7	$ 229.0
Finite-Lived Intangible Assets, Amortization Expense, Next Rolling Twelve Months	35.6
Finite-Lived Intangible Assets, Amortization Expense, Rolling Year Two	39.1
Finite-Lived Intangible Assets, Amortization Expense, Rolling Year Three	33.9
Finite-Lived Intangible Assets, Amortization Expense, Rolling Year Four	26.6
Finite-Lived Intangible Assets, Amortization Expense, Rolling Year Five	21.5
Finite-Lived Intangible Assets, Amortization Expense, Rolling after Year Five	$ 60.0