Derivative Financial Instruments - Notional and Fair Values (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	$ 1,167.8		$ 1,275.8
Derivatives, Liability Fair Value	4,078.7		4,076.4
Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	61,908.6		64,734.1
Interest rate contracts | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	60,311.6	[1],[2]	63,122.0	[1],[2]
Interest rate contracts | Not Designated as Hedging Instrument | Derivatives
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	666.7	[1],[2]	826.2	[1],[2]
Derivatives, Liability Fair Value	804.6	[1],[2]	1,174.3	[1],[2]
Interest rate caps | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	11,800.0		11,800.0
Interest rate caps | Not Designated as Hedging Instrument | Derivatives
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	101.0		162.5
Derivatives, Liability Fair Value	17.7		29.7
Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,407.9		1,456.4
Foreign exchange contracts | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,233.2	[1]	1,281.7	[1]
Foreign exchange contracts | Not Designated as Hedging Instrument | Derivatives
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	21.1	[1]	17.8	[1]
Derivatives, Liability Fair Value	29.2	[1]	43.3	[1]
Equity contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	9,707.4		4,513.5
Equity contracts | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	17,412.7	[1]	11,725.9	[1]
Equity contracts | Not Designated as Hedging Instrument | Derivatives
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	217.6	[1]	172.7	[1]
Derivatives, Liability Fair Value	102.6	[1]	52.9	[1]
Credit contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	3,221.0		3,221.0
Credit contracts | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	3,221.0	[1]	3,221.0	[1]
Credit contracts | Not Designated as Hedging Instrument | Derivatives
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	35.3	[1]	40.5	[1]
Derivatives, Liability Fair Value	12.4	[1]	14.5	[1]
Cash Flow Hedging | Interest rate contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	723.5	[1]	786.0	[1]
Cash Flow Hedging | Interest rate contracts | Designated as Hedging Instrument | Derivatives
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	94.9	[1]	81.0	[1]
Derivatives, Liability Fair Value	0	[1]	0.5	[1]
Cash Flow Hedging | Foreign exchange contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	174.7	[1]	174.7	[1]
Cash Flow Hedging | Foreign exchange contracts | Designated as Hedging Instrument | Derivatives
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	5.5	[1]	6.3	[1]
Derivatives, Liability Fair Value	2.1	[1]	1.6	[1]
Fair Value Hedging | Interest rate contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	873.5	[1]	873.5	[1]
Fair Value Hedging | Interest rate contracts | Designated as Hedging Instrument | Derivatives
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	3.6	[1]	4.8	[1]
Derivatives, Liability Fair Value	62.6	[1]	64.7	[1]
Within fixed maturity investments
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	123.1		126.5
Derivatives, Liability Fair Value	0		0
Within annuity products
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	0		0
Derivatives, Liability Fair Value	2,969.3		2,645.6
Within reinsurance agreements
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	0		0
Derivatives, Liability Fair Value	$ 95.9		$ 79.0

[1] Open derivative contracts are reported as Derivatives assets or liabilities on the Condensed Consolidated Balance Sheets at fair value.

[2] As of March 31, 2014, includes a notional amount, asset fair value and liability fair value for interest rate caps of $11.8 billion, $101.0 and $17.7, respectively. As of December 31, 2013, includes a notional amount, asset fair value and liability fair value for interest rate caps of $11.8 billion, $162.5 and $29.7, respectively.