7. Investing Activities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Available-for-sale debt securities Amortized Cost	$ 2,802.5	$ 2,460.9
Available-for-sale debt securities Gross Unrealized Gains (1)	215.7	133.9
Available-for-sale debt securities Gross Unrealized Losses	(52.0)	(82.7)
Available-for-sale debt securities Fair Value	2,966.2	2,512.1
Available-for-sale debt securities OTTI Recognized in AOCI(2)	(31.8)	(35.9)
U.S. government and agency [Member]
Available-for-sale debt securities Amortized Cost	168.2	162.2
Available-for-sale debt securities Gross Unrealized Gains (1)	5.1	12.4
Available-for-sale debt securities Gross Unrealized Losses	(0.4)	(0.5)
Available-for-sale debt securities Fair Value	172.9	174.1
Available-for-sale debt securities OTTI Recognized in AOCI(2)
State and political subdivision [Member]
Available-for-sale debt securities Amortized Cost	98.7	78.3
Available-for-sale debt securities Gross Unrealized Gains (1)	10.3	5.7
Available-for-sale debt securities Gross Unrealized Losses	(0.6)	(0.5)
Available-for-sale debt securities Fair Value	108.4	83.5
Available-for-sale debt securities OTTI Recognized in AOCI(2)
Foreign government [Member]
Available-for-sale debt securities Amortized Cost	44.4	30.5
Available-for-sale debt securities Gross Unrealized Gains (1)	6.5	1.8
Available-for-sale debt securities Gross Unrealized Losses		(0.4)
Available-for-sale debt securities Fair Value	50.9	31.9
Available-for-sale debt securities OTTI Recognized in AOCI(2)
Corporate [Member]
Available-for-sale debt securities Amortized Cost	1,605.3	1,157.4
Available-for-sale debt securities Gross Unrealized Gains (1)	141.6	84.8
Available-for-sale debt securities Gross Unrealized Losses	(26.7)	(37.5)
Available-for-sale debt securities Fair Value	1,720.2	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	245.0	273.3
Available-for-sale debt securities Gross Unrealized Gains (1)	25.9	12.1
Available-for-sale debt securities Gross Unrealized Losses	(1.4)	(3.9)
Available-for-sale debt securities Fair Value	269.5	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	442.8	538.6
Available-for-sale debt securities Gross Unrealized Gains (1)	19.1	13.3
Available-for-sale debt securities Gross Unrealized Losses	(10.1)	(20.4)
Available-for-sale debt securities Fair Value	451.8	531.5
Available-for-sale debt securities OTTI Recognized in AOCI(2)	(24.1)	(21.6)
CDO/CLO [Member]
Available-for-sale debt securities Amortized Cost	63.5	74.0
Available-for-sale debt securities Gross Unrealized Gains (1)	1.4	0.7
Available-for-sale debt securities Gross Unrealized Losses	(6.0)	(12.2)
Available-for-sale debt securities Fair Value	58.9	62.5
Available-for-sale debt securities OTTI Recognized in AOCI(2)	(6.8)	(8.4)
Other asset-backed [Member]
Available-for-sale debt securities Amortized Cost	134.6	146.6
Available-for-sale debt securities Gross Unrealized Gains (1)	5.8	3.1
Available-for-sale debt securities Gross Unrealized Losses	(6.8)	(7.3)
Available-for-sale debt securities Fair Value	133.6	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

-Name Statement of Financial Accounting Standard (FAS)

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

-Publisher FASB

-Name Accounting Standards Codification

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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 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-Number 115

-Paragraph 16

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

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

-Publisher FASB

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Reference 8: 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

-Section 45

-Paragraph 1

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

-Publisher FASB

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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