Derivative Financial Instruments - Notional and Fair Values (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Derivative assets	$ 449.4		$ 493.4
Derivatives liabilities	190.3		185.7
Fixed maturities
Derivatives, Fair Value [Line Items]
Derivative assets	28.1		29.0
Derivatives liabilities	0		0
Fixed indexed annuities (FIA)
Derivatives, Fair Value [Line Items]
Derivative assets	0		0
Derivatives liabilities	71.3		23.1
Reinsurance Agreements
Derivatives, Fair Value [Line Items]
Derivative assets	0		0
Derivatives liabilities	(24.4)		(54.0)
Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivatives, Notional Amount	27,545.7		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	575.8	[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	26,969.9	[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	15.9	[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]
Derivatives | Designated as Hedging Instrument | Cash flow hedges | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivative assets	94.5	[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	4.4	[1]	2.2	[1]
Derivatives liabilities	0	[1]	0.6	[1]
Derivatives | Not Designated as Hedging Instrument | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivative assets	310.0	[1],[2]	367.6	[1],[2]
Derivatives liabilities	138.7	[1],[2]	206.2	[1],[2]
Derivatives | Not Designated as Hedging Instrument | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivative assets	5.9	[1]	5.5	[1]
Derivatives liabilities	4.7	[1]	9.6	[1]
Derivatives | Not Designated as Hedging Instrument | Equity contract
Derivatives, Fair Value [Line Items]
Derivative assets	0	[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	6.5	[1]	8.1	[1]
Derivatives liabilities	$ 0	[1]	$ 0	[1]

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

[2] .

[3] Less than $0.1.