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Reserves for Unpaid Losses and Loss Adjustment Expenses (Incurred Loss and Allocated LAE, Net of Reinsurance - Specialty Industries - Property) (Details) - Property - Specialty Industries $ in Millions	Dec. 31, 2016 USD ($) reported_claim	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)	Dec. 31, 2007 USD ($)
Claims Development [Line Items]
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 1,279.9
2007
Claims Development [Line Items]
Incurred Loss and Allocated LAE, Net of Reinsurance	94.9	$ 95.1	$ 95.1	$ 95.1	$ 95.3	$ 95.1	$ 94.9	$ 101.3	$ 104.8	$ 110.0
Total IBNR plus expected development on reported claims	$ 0.0
Cumulative number of reported claims | reported_claim	4,828
2008
Claims Development [Line Items]
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 129.7	129.8	130.0	132.7	132.0	129.3	129.6	137.6	$ 147.3
Total IBNR plus expected development on reported claims	$ 0.1
Cumulative number of reported claims | reported_claim	6,603
2009
Claims Development [Line Items]
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 118.6	118.7	118.6	118.8	117.9	118.2	118.6	$ 124.5
Total IBNR plus expected development on reported claims	$ 0.1
Cumulative number of reported claims | reported_claim	6,718
2010
Claims Development [Line Items]
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 131.2	131.4	129.7	130.0	127.2	131.5	$ 131.4
Total IBNR plus expected development on reported claims	$ 0.0
Cumulative number of reported claims | reported_claim	8,617
2011
Claims Development [Line Items]
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 142.5	143.2	143.5	141.1	141.5	$ 138.5
Total IBNR plus expected development on reported claims	$ 0.3
Cumulative number of reported claims | reported_claim	9,704
2012
Claims Development [Line Items]
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 130.1	130.4	126.7	123.8	$ 126.9
Total IBNR plus expected development on reported claims	$ 0.8
Cumulative number of reported claims | reported_claim	9,697
2013
Claims Development [Line Items]
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 143.6	142.9	127.0	$ 125.1
Total IBNR plus expected development on reported claims	$ 1.9
Cumulative number of reported claims | reported_claim	8,085
2014
Claims Development [Line Items]
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 130.1	123.5	$ 123.9
Total IBNR plus expected development on reported claims	$ 3.9
Cumulative number of reported claims | reported_claim	8,352
2015
Claims Development [Line Items]
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 138.9	$ 142.3
Total IBNR plus expected development on reported claims	$ 10.2
Cumulative number of reported claims | reported_claim	8,607
2016
Claims Development [Line Items]
Incurred Loss and Allocated LAE, Net of Reinsurance	$ 120.3
Total IBNR plus expected development on reported claims	$ 32.8
Cumulative number of reported claims | reported_claim	7,429

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Undiscounted amount, after reinsurance, of incurred-but-not-reported (IBNR) liabilities plus expected development on reported claims, for claims and allocated claim adjustment expense for short-duration insurance contracts. Excludes unallocated claim adjustment expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 4D
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=65670685&loc=SL65671317-158438

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Undiscounted amount, after reinsurance, of incurred claims and allocated claim adjustment expense used in claims development for short-duration insurance contracts. Excludes unallocated claim adjustment expense.

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