Fair Value Measurements - Level 3 Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Inputs Reconciliation, Calculation [Roll Forward]
Fixed maturities, including securities pledged, Fair Value	$ 21,500.0		$ 19,200.0
Equity securities, available-for-sale	142.8		144.9
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Inputs Reconciliation, Calculation [Roll Forward]
Fixed maturities, including securities pledged, Fair Value	221.5		248.9
Equity securities, available-for-sale	17.0
Separate Accounts | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Inputs Reconciliation, Calculation [Roll Forward]
Total realized/unrealized gains (losses) included in Net income, Assets	0.3	[1]	0	[1]
Total realized/unrealized gains (losses) included in OCI, Assets	0	[1]	0	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	16.3	[1]	9.8	[1]
Change in unrealized gains (losses) included in earnings	0.6	[1],[2]	0.1	[1],[2]
Equity securities, available-for-sale	16.1	[1]	22.3	[1]
Issuances, Assets	0	[1]	0	[1]
Sales, Assets	(8.3)	[1]	(3.4)	[1]
Settlements, Assets	0	[1]	0	[1]
Transfers in to Level 3, Assets	0	[1],[3]	0	[1],[3]
Transfers out of Level 3, Asset	(8.1)	[1],[3]	(12.6)	[1],[3]
Derivatives, excluding Product Guarantee and Fixed Indexed Annuity | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Inputs Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Asset (Liability) Value	0		(12.6)		(13.6)
Fair Value, Assets (Liabilities) Measured on Recurring Basis, Change in Unrealized Gain (Loss) Included in Earnings	0	[2]	0.6	[2]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset (Liability), Gain (Loss) Included in Earnings	(1.8)		0.8
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset (Liability), Gain (Loss) Included in Other Comprehensive Income (Loss)	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset (Liability), Purchases	0		0.2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset (Liability), Issues	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset (Liability), Sales	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset (Liability), Settlements	14.4		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset (Liability) Transfers Into Level 3	0	[3]	0	[3]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset (Liability), Transfers out of Level 3	0	[3]	0	[3]
Product guarantees | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Inputs Reconciliation, Calculation [Roll Forward]
Total realized/unrealized gains (losses) included in Net income, Liability	124.5	[4]	(212.5)	[4]
Total realized/unrealized gains (losses) included in OCI, Liability	0	[4]	0	[4]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases	(5.5)	[4]	(5.5)	[4]
Issues, Liability	0	[4]	0	[4]
Sales, Liability	0	[4]	0	[4]
Settlements, Liability	0	[4]	0	[4]
Transfers Into Level 3, Liability	0	[3],[4]	0	[3],[4]
Transfers out of Level 3, Liability	0	[3],[4]	0	[3],[4]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	(102.0)	[4]	(221.0)	[4]	(3.0)	[4]
Change in unrealized gains (losses) included in earnings	0	[2],[4]	0	[2],[4]
Fixed indexed annuities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Inputs Reconciliation, Calculation [Roll Forward]
Total realized/unrealized gains (losses) included in Net income, Liability	(4.1)	[4]	(3.6)	[4]
Total realized/unrealized gains (losses) included in OCI, Liability	0	[4]	0	[4]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases	0	[4]	(7.1)	[4]
Issues, Liability	0	[4]	0	[4]
Sales, Liability	0	[4]	0	[4]
Settlements, Liability	0	[4]	0	[4]
Transfers Into Level 3, Liability	0	[3],[4]	0	[3],[4]
Transfers out of Level 3, Liability	0	[3],[4]	0	[3],[4]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	(20.4)	[4]	(16.3)	[4]	(5.6)	[4]
Change in unrealized gains (losses) included in earnings	0	[2],[4]	0	[2],[4]
U.S. corporate, state and municipalities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Inputs Reconciliation, Calculation [Roll Forward]
Fixed maturities, including securities pledged	129.1		11.2
Total realized/unrealized gains (losses) included in Net income, Assets	(0.3)		(0.3)
Total realized/unrealized gains (losses) included in OCI, Assets	1.4		(6.7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0.4		19.0
Change in unrealized gains (losses) included in earnings	(0.4)	[2]	(0.3)	[2]
Issuances, Assets	0		0
Sales, Assets	0		0
Settlements, Assets	(7.9)		(43.3)
Transfers in to Level 3, Assets	38.3	[3]	135.8	[3]
Transfers out of Level 3, Asset	(3.6)	[3]	0	[3]
Fixed maturities, including securities pledged, Fair Value	154.6		129.1
Foreign securities government
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Inputs Reconciliation, Calculation [Roll Forward]
Fixed maturities, including securities pledged, Fair Value	496.0	[5]	345.2	[5]
Foreign securities government | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Inputs Reconciliation, Calculation [Roll Forward]
Fixed maturities, including securities pledged	51.1		11.4
Total realized/unrealized gains (losses) included in Net income, Assets	0.9		0.5
Total realized/unrealized gains (losses) included in OCI, Assets	4.2		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0		30.9
Change in unrealized gains (losses) included in earnings	0	[2]	(0.8)	[2]
Issuances, Assets	0		0
Sales, Assets	(5.7)		(19.7)
Settlements, Assets	(12.5)		(1.5)
Transfers in to Level 3, Assets	20.7	[3]	29.9	[3]
Transfers out of Level 3, Asset	(25.7)	[3]	(0.4)	[3]
Fixed maturities, including securities pledged, Fair Value	24.6	[5]	51.1	[5]
Residential mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Inputs Reconciliation, Calculation [Roll Forward]
Fixed maturities, including securities pledged, Fair Value	2,357.5		2,247.1
Residential mortgage-backed | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Inputs Reconciliation, Calculation [Roll Forward]
Fixed maturities, including securities pledged	41.0		254.7
Total realized/unrealized gains (losses) included in Net income, Assets	0.7		(3.0)
Total realized/unrealized gains (losses) included in OCI, Assets	(2.7)		(1.7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	2.3		57.1
Change in unrealized gains (losses) included in earnings	(0.1)	[2]	(0.9)	[2]
Issuances, Assets	0		0
Sales, Assets	(6.0)		(38.5)
Settlements, Assets	0		(8.1)
Transfers in to Level 3, Assets	0	[3]	5.3	[3]
Transfers out of Level 3, Asset	(31.6)	[3]	(228.2)	[3]
Fixed maturities, including securities pledged, Fair Value	9.1		41.0
Asset-backed Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Inputs Reconciliation, Calculation [Roll Forward]
Fixed maturities, including securities pledged	27.7		247.7
Total realized/unrealized gains (losses) included in Net income, Assets	1.1		(26.8)
Total realized/unrealized gains (losses) included in OCI, Assets	(2.5)		(15.8)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0		0
Change in unrealized gains (losses) included in earnings	0.8	[2]	(3.5)	[2]
Issuances, Assets	0		0
Sales, Assets	0		(119.7)
Settlements, Assets	(1.9)		(8.7)
Transfers in to Level 3, Assets	3.8	[3]	0	[3]
Transfers out of Level 3, Asset	0	[3]	(80.6)	[3]
Fixed maturities, including securities pledged, Fair Value	33.2		27.7
Fixed maturities, available-for-sale, including securities pledged | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Inputs Reconciliation, Calculation [Roll Forward]
Fixed maturities, including securities pledged	248.9		525.0
Total realized/unrealized gains (losses) included in Net income, Assets	2.4		(29.6)
Total realized/unrealized gains (losses) included in OCI, Assets	0.4		(24.2)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	2.7		107.0
Change in unrealized gains (losses) included in earnings	0.3	[2]	(5.5)	[2]
Issuances, Assets	0		0
Sales, Assets	(11.7)		(177.9)
Settlements, Assets	(22.3)		(61.6)
Transfers in to Level 3, Assets	62.8	[3]	171.0	[3]
Transfers out of Level 3, Asset	(60.9)	[3]	(309.2)	[3]
Equity securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Inputs Reconciliation, Calculation [Roll Forward]
Total realized/unrealized gains (losses) included in Net income, Assets	(0.2)		0.1
Total realized/unrealized gains (losses) included in OCI, Assets	0.2		(0.1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0.8		4.3
Change in unrealized gains (losses) included in earnings	(0.5)	[2]	0	[2]
Equity securities, available-for-sale	19.0		27.7
Issuances, Assets	0		0
Sales, Assets	(2.4)		(4.2)
Settlements, Assets	0		0
Transfers in to Level 3, Assets	0.3	[3]	0	[3]
Transfers out of Level 3, Asset	(0.3)	[3]	(9.0)	[3]
Equity securities, available-for-sale			$ 19.0

[1] The investment income and realized gains (losses) and change in unrealized gains (losses) included in net income (loss) for separate account assets are offset by an equal amount for separate account liabilities, which result in a net zero impact on net income (loss) for the Company.

[2] For financial instruments still held as of December 31, amounts are included in Net investment income and Other net realized capital gains (losses) in the Consolidated Statements of Operations.

[3] The Company’s policy is to recognize transfers in and transfers out as of the beginning of the reporting period.

[4] All gains and losses on Level 3 are classified as realized gains (losses) for the purpose of this disclosure because it is impracticable to track realized and unrealized gains (losses) separately on a contract-by-contract basis. These amounts are included in Other net realized capital gains (losses) in the Consolidated Statements of Operations.

[5] Primarily U.S. dollar denominated.