Investing Activities Schedule of Available-for-sale Securities Reconciliation (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Total available-for-sale debt securities
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales	$ 141.0	$ 90.0	$ 160.0
Proceeds from maturities/repayments	250.5	286.1	285.3
Gross investment gains from sales	6.1	11.3	22.8
Gross investment losses from sales	(2.4)	(0.4)	(0.7)
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales	1.0	0	0
Gross investment gains from sales	0	0	0
Gross investment losses from sales	$ (0.1)	$ 0	$ 0

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563

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+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26853-111562

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

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-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

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-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585

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

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