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]
Derivative assets	$ 441.4		$ 493.4
Derivatives liabilities	190.6		185.7
Fixed maturities
Derivatives, Fair Value [Line Items]
Derivative assets	28.5		29.0
Derivatives liabilities	0		0
Fixed indexed annuities (FIA)
Derivatives, Fair Value [Line Items]
Derivative assets	0		0
Derivatives liabilities	42.3		23.1
Reinsurance Agreements
Derivatives, Fair Value [Line Items]
Derivative assets	0		0
Derivatives liabilities	(30.7)		(54.0)
Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivatives, Notional Amount	23,075.5		22,206.0
Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivatives, Notional Amount	181.3		197.1
Credit contracts
Derivatives, Fair Value [Line Items]
Derivatives, Notional Amount	384.0		384.0
Designated as Hedging Instrument | Cash flow hedges | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivatives, Notional Amount	700.8	[1]	763.3	[1]
Designated as Hedging Instrument | Cash flow hedges | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivatives, Notional Amount	51.2	[1]	51.2	[1]
Not Designated as Hedging Instrument | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivatives, Notional Amount	22,374.7	[1],[2]	21,442.7	[1],[2]
Not Designated as Hedging Instrument | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivatives, Notional Amount	130.1	[1]	145.9	[1]
Not Designated as Hedging Instrument | Equity contract
Derivatives, Fair Value [Line Items]
Derivatives, Notional Amount	11.5	[1]	9.1	[1]
Not Designated as Hedging Instrument | Credit contracts
Derivatives, Fair Value [Line Items]
Derivatives, Notional Amount	384.0	[1]	384.0	[1]
Not Designated as Hedging Instrument | Interest rate caps
Derivatives, Fair Value [Line Items]
Derivatives, Notional Amount	11,800.0		11,800.0
Derivatives | Designated as Hedging Instrument | Cash flow hedges | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivative assets	94.9	[1]	81.0	[1]
Derivatives liabilities	0	[1]	0.2	[1]
Derivatives | Designated as Hedging Instrument | Cash flow hedges | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivative assets	1.9	[1]	2.2	[1]
Derivatives liabilities	0.8	[1]	0.6	[1]
Derivatives | Not Designated as Hedging Instrument | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivative assets	303.3	[1],[2]	367.6	[1],[2]
Derivatives liabilities	172.4	[1],[2]	206.2	[1],[2]
Derivatives | Not Designated as Hedging Instrument | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivative assets	5.3	[1]	5.5	[1]
Derivatives liabilities	5.8	[1]	9.6	[1]
Derivatives | Not Designated as Hedging Instrument | Equity contract
Derivatives, Fair Value [Line Items]
Derivative assets	0.1	[1]	0	[1],[3]
Derivatives liabilities	0	[1]	0	[1]
Derivatives | Not Designated as Hedging Instrument | Credit contracts
Derivatives, Fair Value [Line Items]
Derivative assets	7.4	[1]	8.1	[1]
Derivatives liabilities	0	[1]	0	[1]
Derivatives | Not Designated as Hedging Instrument | Interest rate caps
Derivatives, Fair Value [Line Items]
Derivative assets	101.1		162.5
Derivatives liabilities	$ 17.7		$ 29.7

[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, $101.1 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.

[3] Less than $0.1.