Derivative Financial Instruments - Net Realized Gains (Losses) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	$ 314.6	$ (466.0)	$ (379.2)		$ (1,512.4)
Other Net Realized Capital Gains (Losses) | Interest rate contracts | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	82.9	(105.6)	443.8	[1]	(915.0)	[1]
Other Net Realized Capital Gains (Losses) | Foreign exchange contracts | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	66.3	(46.3)	63.3	[1]	71.3	[1]
Other Net Realized Capital Gains (Losses) | Equity contracts | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	15.0	(493.0)	(512.0)	[1]	(1,644.9)	[1]
Other Net Realized Capital Gains (Losses) | Credit contracts | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	2.2	7.1	3.1	[1]	18.2	[1]
Other Net Realized Capital Gains (Losses) | Managed Custody Guarantees [Member] | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	0	1.0	0.1		1.1
Within fixed maturity investments | Other Net Realized Capital Gains (Losses)
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	(1.1)	(16.1)	(8.3)	[1]	(89.6)	[1]
Within annuity products | Other Net Realized Capital Gains (Losses)
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	127.7	183.6	(298.1)	[1]	943.3	[1]
Within reinsurance agreements | Policyholder Benefits
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	20.1	9.3	(61.3)	[2]	82.5	[2]
Cash Flow Hedging | Other Net Realized Capital Gains (Losses) | Interest rate contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	0.3	0	0.6	[3]	0.1	[3]
Cash Flow Hedging | Other Net Realized Capital Gains (Losses) | Foreign exchange contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	0.5	0.1	1.5	[3]	0.1	[3]
Fair Value Hedging | Other Net Realized Capital Gains (Losses) | Interest rate contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	$ 0.7	$ (6.1)	$ (11.9)	[3]	$ 20.5	[3]

[1] Changes in value are included in Other net realized capital gains (losses) in the Condensed Consolidated Statements of Operations.

[2] Changes in value are included in Policyholder benefits in the Condensed Consolidated Statements of Operations.

[3] Changes in value for effective fair value hedges are recorded in Other net realized capital gains (losses). Changes in fair value upon disposal for effective cash flow hedges are amortized through Net investment income and the ineffective portion is recorded in Other net realized capital gains (losses) in the Condensed Consolidated Statements of Operations. For the three and nine months ended September 30, 2014 and 2013, ineffective amounts were immaterial.