Catastrophe Reinsurance - Catastrophe Losses and LAE (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	$ 1,103.2	$ 908.3	$ 991.9
Catastrophe Loss and LAE Reserves, (Unfavorable) Favorable Development	(20.1)	(57.1)	(64.6)
Catastrophe [Member]
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	60.5	83.8	36.2
Catastrophe Loss and LAE Reserves, (Unfavorable) Favorable Development	(7.8)	(14.7)	(14.5)
Property and Casualty Insurance [Member] | Catastrophe [Member]
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	56.6	80.7	34.6
Catastrophe Loss and LAE Reserves, (Unfavorable) Favorable Development	(7.9)	(15.8)	(12.5)
Life and Health Insurance [Member] | Catastrophe [Member]
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	3.9	3.1	1.6
Catastrophe Loss and LAE Reserves, (Unfavorable) Favorable Development	$ 0.1	$ 1.1	$ (2.0)