Consolidated Investment Products (Beginning And Ending Fair Value Measurements For Level 3 Assets And Liabilities) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net unrealized gains/losses attributable to investments			$ 4.2
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance (Asset)	$ 0.0	$ 388.6	343.1	$ 388.6	$ 363.9
Purchases (Asset)	0.0		17.1
Sales (Asset)	0.0		(27.0)
Gains and losses included in the Condensed Consolidated Statements of Income	0.0		(2.5)
Transfers to Levels 1 and 2	0.0		(8.4)
Ending balance (Asset)	0.0	388.6	343.1
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance (Liability)	0.0		(5,149.6)
Purchases (Liability)	0.0		0.0
Sales (Liability)	0.0		0.0
Net unrealized gains and losses included in other gains and losses	0.0		0.0
Transfers to Levels 1 and 2	0.0		0.0
Ending balance (Liability)	0.0	$ 0.0	0.0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers to Levels 1 and 2	7.8
Accounting Standards Update 2014-13 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption					$ (17.6)
Accounting Standards Update 2014-13 [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Adjustment for adoption (Asset)	0.0		0.0
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Adjustment for adoption (Liability)	0.0		(5,149.6)
Accounting Standards Update 2015-02 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption				$ (733.5)
Accounting Standards Update 2015-02 [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Adjustment for adoption (Asset)	(388.6)		0.0
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Adjustment for adoption (Liability)	$ 0.0		$ 0.0