Derivative Financial Instruments Derivative Financial Instruments - Offsetting Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Offsetting Assets and Liabilities [Line Items]
Collateralized loan obligations notes, at fair value using the fair value option	$ 5,955.6		$ 5,161.6
Derivatives, Asset Fair Value	1,094.3		1,147.3
Derivatives, Liability Fair Value	907.5		1,330.9
Counterparty netting, Assets	(612.2)	[1]	(701.0)	[1]
Counterparty netting, Liabilities	(612.2)	[1]	(701.0)	[1]
Cash collateral netting, Assets	(352.3)	[1]	(241.7)	[1]
Cash collateral netting, Liabilities	(41.7)	[1]	(15.7)	[1]
Securities collateral netting, Assets	(30.0)	[1]	(35.9)	[1]
Securities collateral netting, Liabilities	(169.4)	[1]	(479.1)	[1]
Net receivables/payables, Assets	99.8		168.7
Net receivables/payables, Liabilities	84.2		135.1
Credit contracts
Offsetting Assets and Liabilities [Line Items]
Derivative, Notional Amount	3,221.0		3,221.0
Derivatives, Asset Fair Value	46.0		40.5
Derivatives, Liability Fair Value	26.8		14.5
Equity contracts
Offsetting Assets and Liabilities [Line Items]
Derivative, Notional Amount	9,781.5		4,513.5
Derivatives, Asset Fair Value	211.3		170.7
Derivatives, Liability Fair Value	62.9		32.0
Foreign exchange contracts
Offsetting Assets and Liabilities [Line Items]
Derivative, Notional Amount	1,418.2		1,456.4
Derivatives, Asset Fair Value	18.1		24.1
Derivatives, Liability Fair Value	34.1		44.9
Interest rate contracts
Offsetting Assets and Liabilities [Line Items]
Derivative, Notional Amount	64,358.9		64,734.1
Derivatives, Asset Fair Value	818.9		912.0
Derivatives, Liability Fair Value	783.7		1,239.5
Securities pledged as collateral
Offsetting Assets and Liabilities [Line Items]
Collateralized loan obligations notes, at fair value using the fair value option	31.3		51.3
Fair value of securities delivered as collateral	$ 751.3		$ 1,000.0

[1] Represents the netting of receivable balances with payable balances, net of collateral, for the same counterparty under eligible netting agreements.