Schdeule of Level 3 Assets and Liabilities by Pricing Source (Details) (Level 3, USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Embedded derivatives
Level 3 Assets and Liabilities by Pricing Source:
Total liabilities Internal	$ 74.8	[1]	$ 79.5	[1]
Total liabilities External	0	[2]	0	[2]
Total liabilities	74.8		79.5
Total liabilities
Level 3 Assets and Liabilities by Pricing Source:
Total liabilities Internal	74.8	[1]	79.5	[1]
Total liabilities External	0	[2]	0	[2]
Total liabilities	74.8		79.5
U.S. government and agency
Level 3 Assets and Liabilities by Pricing Source:
Total assets Internal	58.8	[1],[3]	25.9	[1],[3]
Total assets External	0	[2],[3]	0	[2],[3]
Total assets	58.8	[3]	25.9	[3]	31.7	[3]
State and political subdivision
Level 3 Assets and Liabilities by Pricing Source:
Total assets Internal	45.4	[1]	58.0	[1]
Total assets External	88.4	[2]	58.1	[2]
Total assets	133.8		116.1		48.7
Foreign government
Level 3 Assets and Liabilities by Pricing Source:
Total assets Internal	0	[1]	0	[1]
Total assets External	3.3	[2]	8.0	[2]
Total assets	3.3		8.0		3.1
Corporate
Level 3 Assets and Liabilities by Pricing Source:
Total assets Internal	874.1	[1]	649.6	[1]
Total assets External	228.2	[2]	151.9	[2]
Total assets	1,102.3		801.5		513.8
CMBS
Level 3 Assets and Liabilities by Pricing Source:
Total assets Internal	0	[1]	0	[1]
Total assets External	31.9	[2]	19.3	[2]
Total assets	31.9		19.3		35.4
RMBS
Level 3 Assets and Liabilities by Pricing Source:
Total assets Internal	0	[1]	0	[1]
Total assets External	175.9	[2]	222.6	[2]
Total assets	175.9		222.6		268.0
CDO/CLO
Level 3 Assets and Liabilities by Pricing Source:
Total assets Internal	0	[1]	3.4	[1]
Total assets External	70.9	[2]	53.4	[2]
Total assets	70.9		56.8		62.5
Other asset-backed
Level 3 Assets and Liabilities by Pricing Source:
Total assets Internal	11.3	[1]	2.8	[1]
Total assets External	71.0	[2]	77.3	[2]
Total assets	82.3		80.1		81.2
Total available-for-sale debt securities
Level 3 Assets and Liabilities by Pricing Source:
Total assets Internal	989.6	[1]	739.7	[1]
Total assets External	669.6	[2]	590.6	[2]
Total assets	1,659.2		1,330.3		1,044.4
Related party reinsurance derivative asset
Level 3 Assets and Liabilities by Pricing Source:
Total assets Internal	0	[1]	0	[1]
Total assets External	0	[2]	0	[2]
Total assets	0		0		3.5
Fair value investments
Level 3 Assets and Liabilities by Pricing Source:
Total assets Internal	0.8	[1]	0.8	[1]
Total assets External	34.8	[2]	21.9	[2]
Total assets	35.6		22.7		27.5
Total assets
Level 3 Assets and Liabilities by Pricing Source:
Total assets Internal	990.4	[1]	740.5	[1]
Total assets External	704.4	[2]	612.5	[2]
Total assets	$ 1,694.8		$ 1,353.0		$ 1,075.4

[1] Represents valuations reflecting both internally-derived and market inputs, as well as third-party information or quotes.

[2] Represents unadjusted prices from independent pricing services, third-party financial statements and independent indicative broker quotes where pricing inputs are not readily available.

[3] Includes securities whose underlying collateral is an obligation of a U.S. government entity.