Acquisitions (Purchase Consideration) (Details) - TWG Holdings Limited $ / shares in Units, $ in Millions	May 31, 2018 USD ($) $ / shares shares
Business Acquisition [Line Items]
Common stock shares issued to TWG equityholders \| shares	10,399,862
Volume weighted average common share price of Assurant, Inc. on May 31, 2018 \| $ / shares	$ 93.80
Share issuance consideration	$ 975.5
Aggregate cash consideration	894.9
Repayment of pre-existing TWG debt	595.9
Total acquisition consideration	$ 2,466.3

Number of shares of equity interests issued or issuable to acquire entity.

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