Derivative Financial Instruments Derivative Financial Instruments - Offsetting Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Offsetting Assets and Liabilities [Line Items]
Collateralized loan obligations notes, at fair value using the fair value option	$ 5,525.5		$ 5,161.6
Derivatives, Asset Fair Value	1,039.2		1,147.3
Derivatives, Liability Fair Value	955.5		1,330.9
Counterparty netting, Assets	(589.5)	[1]	(701.0)	[1]
Counterparty netting, Liabilities	(589.5)	[1]	(701.0)	[1]
Cash collateral netting, Assets	(326.6)	[1]	(241.7)	[1]
Cash collateral netting, Liabilities	(13.6)	[1]	(15.7)	[1]
Securities collateral netting, Assets	(43.7)	[1]	(35.9)	[1]
Securities collateral netting, Liabilities	(260.9)	[1]	(479.1)	[1]
Net receivables/payables, Assets	79.4		168.7
Net receivables/payables, Liabilities	91.5		135.1
Credit contracts
Offsetting Assets and Liabilities [Line Items]
Derivative, Notional Amount	3,221.0		3,221.0
Derivatives, Asset Fair Value	35.3		40.5
Derivatives, Liability Fair Value	12.4		14.5
Equity contracts
Offsetting Assets and Liabilities [Line Items]
Derivative, Notional Amount	9,707.4		4,513.5
Derivatives, Asset Fair Value	212.1		170.7
Derivatives, Liability Fair Value	44.6		32.0
Foreign exchange contracts
Offsetting Assets and Liabilities [Line Items]
Derivative, Notional Amount	1,407.9		1,456.4
Derivatives, Asset Fair Value	26.6		24.1
Derivatives, Liability Fair Value	31.3		44.9
Interest rate contracts
Offsetting Assets and Liabilities [Line Items]
Derivative, Notional Amount	61,908.6		64,734.1
Derivatives, Asset Fair Value	765.2		912.0
Derivatives, Liability Fair Value	867.2		1,239.5
Securities pledged as collateral
Offsetting Assets and Liabilities [Line Items]
Fair value of securities delivered as collateral	$ 821.9		$ 1,000.0

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