Investments - Proceeds From Sales of Available-For-Sale Securities and the Gross Realized Gains and Gross Realized Losses (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale securities, proceeds and realized gains (losses) included in earnings
Proceeds from sales	$ 177.7
Proceeds from sales		$ 218.7	$ 1,939.4
Gross realized gains	6.9
Gross realized gains		7.1	168.9
Gross realized losses	$ (2.6)
Gross realized losses		(0.4)	$ (19.9)
Other information
Average period of time for which securities were traded continuously at a price below book value for securities sold at a loss	3 months
Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Assurant Employee Benefits
Available-for-sale securities, proceeds and realized gains (losses) included in earnings
Gross realized gains		145.6
Gross realized losses		$ (15.9)

Represents the average period of time for which securities were traded continuously at a price below book value.

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Debt Securities, Available-for-sale, Other Information [Abstract]

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

+ References

No definition available.

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

+ References

No definition available.

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- Definition

Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

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Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of cash inflow from sale, maturity, prepayment and call of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3151-108585

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

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-Publisher FASB
-Name Accounting Standards Codification
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