7. Investing Activities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Available-for-sale debt securities Amortized Cost	$ 3,043.0	$ 2,460.9
Available-for-sale debt securities Gross Unrealized Gains	219.0	133.9
Available-for-sale debt securities Gross Unrealized Losses(1)	(44.8)	(82.7)
Available-for-sale debt securities Fair Value	3,217.2	2,512.1
Available-for-sale debt securities OTTI Recognized in AOCI(2)	(21.4)	(35.9)
U.S. government and agency [Member]
Available-for-sale debt securities Amortized Cost	280.7	162.2
Available-for-sale debt securities Gross Unrealized Gains	4.8	12.4
Available-for-sale debt securities Gross Unrealized Losses(1)	(0.4)	(0.5)
Available-for-sale debt securities Fair Value	285.1	174.1
Available-for-sale debt securities OTTI Recognized in AOCI(2)
State and political subdivision [Member]
Available-for-sale debt securities Amortized Cost	120.5	78.3
Available-for-sale debt securities Gross Unrealized Gains	10.9	5.7
Available-for-sale debt securities Gross Unrealized Losses(1)	(0.5)	(0.5)
Available-for-sale debt securities Fair Value	130.9	83.5
Available-for-sale debt securities OTTI Recognized in AOCI(2)	(0.2)
Foreign government [Member]
Available-for-sale debt securities Amortized Cost	44.4	30.5
Available-for-sale debt securities Gross Unrealized Gains	7.4	1.8
Available-for-sale debt securities Gross Unrealized Losses(1)		(0.4)
Available-for-sale debt securities Fair Value	51.8	31.9
Available-for-sale debt securities OTTI Recognized in AOCI(2)
Corporate [Member]
Available-for-sale debt securities Amortized Cost	1,776.9	1,157.4
Available-for-sale debt securities Gross Unrealized Gains	144.6	84.8
Available-for-sale debt securities Gross Unrealized Losses(1)	(24.0)	(37.5)
Available-for-sale debt securities Fair Value	1,897.5	1,204.7
Available-for-sale debt securities OTTI Recognized in AOCI(2)	(1.5)	(1.5)
Commercial mortgage-backed (CMBS) [Member]
Available-for-sale debt securities Amortized Cost	229.6	273.3
Available-for-sale debt securities Gross Unrealized Gains	26.0	12.1
Available-for-sale debt securities Gross Unrealized Losses(1)	(1.6)	(3.9)
Available-for-sale debt securities Fair Value	254.0	281.5
Available-for-sale debt securities OTTI Recognized in AOCI(2)	(0.6)	(5.1)
Residential mortgage-backed (RMBS) [Member]
Available-for-sale debt securities Amortized Cost	412.6	538.6
Available-for-sale debt securities Gross Unrealized Gains	17.5	13.3
Available-for-sale debt securities Gross Unrealized Losses(1)	(7.6)	(20.4)
Available-for-sale debt securities Fair Value	422.5	531.5
Available-for-sale debt securities OTTI Recognized in AOCI(2)	(13.8)	(21.6)
CDO/CLO [Member]
Available-for-sale debt securities Amortized Cost	59.2	74.0
Available-for-sale debt securities Gross Unrealized Gains	1.8	0.7
Available-for-sale debt securities Gross Unrealized Losses(1)	(4.2)	(12.2)
Available-for-sale debt securities Fair Value	56.8	62.5
Available-for-sale debt securities OTTI Recognized in AOCI(2)	(6.5)	(8.4)
Other asset-backed [Member]
Available-for-sale debt securities Amortized Cost	119.1	146.6
Available-for-sale debt securities Gross Unrealized Gains	6.0	3.1
Available-for-sale debt securities Gross Unrealized Losses(1)	(6.5)	(7.3)
Available-for-sale debt securities Fair Value	118.6	142.4
Available-for-sale debt securities OTTI Recognized in AOCI(2)	$ 1.2	$ 0.7

Amount of debt securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

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Reference 10: http://www.xbrl.org/2003/role/presentationRef

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+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details