Fair Value Of Assets And Liabilities (Reconciliation Of Balance, Fair Value Measurement, Level 3) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance			$ 7,962.2				$ 9,102.2
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance (Liability)	$ 0.0	$ 0.0		$ 0.0	$ 0.0	$ (5,149.6)
Beginning balance (Asset)	0.0	(388.6)		(343.1)	(388.6)	(363.9)
Purchases (Liability)	0.0	0.0		0.0		0.0
Purchases (Assets)	(23.9)	(23.9)		(2.1)		(19.2)
Net unrealized gains and losses included in other gains and losses	0.0	0.0		0.0		0.0
Gains and losses included in the Condensed Consolidated Statements of Income	0.0	0.0		22.9		(25.4)
Sales (Asset)	0.0	0.0		(14.2)		(41.2)
Ending balance (Liability)	0.0	0.0	0.0	0.0	0.0	0.0
Ending balance (Asset)	(23.9)	0.0	(388.6)	(308.1)	(23.9)	(308.1)
Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance		(77.2)	(83.9)
Liability [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance (Liability)	(77.2)	(83.9)		(119.3)	(83.9)	0.0
Purchases (Liability)			(119.3)	0.0		(119.3)
Returns of capital	0.0			0.0	0.0	0.0
Net unrealized gains and losses included in other gains and losses	(15.1)				(11.6)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)	0.0				0.0
Settlements (Liability)	3.0			1.5	6.2	1.5
Ending balance (Liability)	(89.3)	(77.2)	(83.9)	(117.8)	(89.3)	(117.8)
Collateralized Loan Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance		11.8	12.9
Collateralized Loan Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance (Asset)	(11.8)	(1.4)		(2.5)	(1.4)	(3.4)
Purchases (Assets)				0.0		0.0
Returns of capital	(0.8)			0.0	(1.3)	(0.1)
Gains and losses included in the Condensed Consolidated Statements of Income	0.0				0.0
Net unrealized gains and losses included in accumulated other comprehensive income/(loss)	0.5				(0.1)
Sales (Asset)	0.0			(1.2)	0.0	(2.0)
Ending balance (Asset)	(11.5)	(11.8)	(1.4)	(1.3)	(11.5)	(1.3)
Other Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance		4.3	5.9
Other Debt Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance (Asset)	(4.3)	(5.9)		(6.3)	(5.9)	(6.3)
Purchases (Assets)				0.0		0.0
Returns of capital	(1.0)			0.0	(2.6)	0.0
Gains and losses included in the Condensed Consolidated Statements of Income	0.0				0.0
Net unrealized gains and losses included in accumulated other comprehensive income/(loss)	0.0				0.0
Sales (Asset)	0.0			0.0	0.0	0.0
Ending balance (Asset)	$ (3.3)	(4.3)	(5.9)	$ (6.3)	$ (3.3)	$ (6.3)
Accounting Standards Update 2015-02 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			(733.5)
Accounting Standards Update 2015-02 [Member] | Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		0.0	0.0
Accounting Standards Update 2015-02 [Member] | Collateralized Loan Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		0.0	11.5
Accounting Standards Update 2015-02 [Member] | Other Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 0.0	$ 0.0