Business Segments - Segment Assets (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Assets	$ 8,036.1	$ 7,833.4
Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Assets	2,749.0	2,486.1
Life and Health Insurance [Member]
Segment Reporting Information [Line Items]
Assets	4,733.9	4,810.6
Corporate and Other, Net [Member]
Segment Reporting Information [Line Items]
Assets	$ 553.2	$ 536.7