Fair Value Of Assets And Liabilities - Fair Value Of Financial Instruments Held By Consolidated Investments (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 940.5	$ 1,049.0	$ 1,017.1
Foreign time deposits	25.8	32.0
Policyholder payables	(9,137.3)	(10,835.6)
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	940.5	1,049.0
Equity investments	334.1	432.5
Foreign time deposits	25.8	32.0
Assets held for policyholders	9,137.3	10,835.6
Policyholder payables	(9,137.3)	(10,835.6)
Contingent consideration liability	(33.6)	(60.2)
Long-term debt	$ (2,806.9)	$ (2,281.5)