Fair Value Of Assets And Liabilities - Fair Value Of Financial Instruments Held By Consolidated Investments (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 987.1	$ 1,049.0	$ 1,199.4
Foreign time deposits	27.3	32.0
Policyholder payables	(8,020.9)	(10,835.6)
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	987.1	1,049.0
Equity investments	314.8	432.5
Foreign time deposits	27.3	32.0
Assets held for policyholders	8,020.9	10,835.6
Policyholder payables	(8,020.9)	(10,835.6)
Contingent consideration liability	$ (29.3)	$ (60.2)