Fair Value Of Assets And Liabilities (Tri-Level Hierarchy, Carrying Value) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments		$ 85.2
Equity investments	$ 309.2	346.6
Assets held for policyholders	12,268.2	12,444.5
Total	12,981.6	13,682.5
Total	(45.4)	(57.4)
Foreign time deposits		28.6
Equity Method Investments	308.7	277.3
Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations, Fair Value Disclosure	(45.4)	(57.4)
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	404.2	875.5
Seed money
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments	202.3	243.0
Deferred Compensation Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments	90.4	92.3
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments	16.5	11.3
CLOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments		6.0
Other debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments		9.9
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for policyholders	12,268.2	12,444.5
Total	12,981.6	13,666.6
Total	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations, Fair Value Disclosure	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	404.2	875.5
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Seed money
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments	202.3	243.0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Deferred Compensation Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments	90.4	92.3
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments	16.5	11.3
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | CLOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments		0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments		0.0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for policyholders	0.0	0.0
Total	0.0	6.0
Total	0.0	0.0
Significant Other Observable Inputs (Level 2) [Member] | Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations, Fair Value Disclosure	0.0	0.0
Significant Other Observable Inputs (Level 2) [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0.0	0.0
Significant Other Observable Inputs (Level 2) [Member] | Seed money
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments	0.0	0.0
Significant Other Observable Inputs (Level 2) [Member] | Deferred Compensation Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments	0.0	0.0
Significant Other Observable Inputs (Level 2) [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments	0.0	0.0
Significant Other Observable Inputs (Level 2) [Member] | CLOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments		6.0
Significant Other Observable Inputs (Level 2) [Member] | Other debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments		0.0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for policyholders	0.0	0.0
Total	0.0	9.9
Total	(45.4)	(57.4)
Significant Unobservable Inputs (Level 3) [Member] | Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations, Fair Value Disclosure	(45.4)	(57.4)
Significant Unobservable Inputs (Level 3) [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | Seed money
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments	0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | Deferred Compensation Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments	0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments	$ 0.0	0.0
Significant Unobservable Inputs (Level 3) [Member] | CLOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments		0.0
Significant Unobservable Inputs (Level 3) [Member] | Other debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments		$ 9.9