Loss and Loss Adjustment Expense Reserves (Loss and Loss Adjustment Expense) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Loss and Loss Adjustment Expense Reserve
Gross beginning balance	$ 3,053.3	$ 3,057.9	$ 3,079.3	$ 3,168.9
Less beginning reinsurance recoverable on unpaid losses	(433.2)	(388.6)	(428.1)	(429.1)
Net loss and LAE reserves	2,620.1	2,669.3	2,651.2	2,739.8
Loss and LAE reserves acquired	0	0	0	21.3
Loss and LAE reserves consolidated — SSIE	0	0	13.6	0
Loss and LAE incurred relating to current year losses	301.2	289.9	820.1	822.8
Net (favorable) and unfavorable loss reserve development	(12.1)	(11.6)	(19.0)	(25.6)
Total incurred losses and LAE	289.1	278.3	801.1	797.2
Accretion of fair value adjustment to net loss and LAE reserves	0.1	0.2	0.5	1.5
Foreign currency translation adjustment to net loss and LAE reserves	(23.5)	12.3	(22.2)	(1.9)
Current year losses	(86.2)	(90.0)	(187.0)	(209.9)
Prior year losses	(207.4)	(178.0)	(665.0)	(655.9)
Total loss and LAE payments	(293.6)	(268.0)	(852.0)	(865.8)
Net ending balance	2,592.2	2,692.1	2,592.2	2,692.1
Plus ending reinsurance recoverable on unpaid losses	430.7	416.0	430.7	416.0
Gross ending balance	$ 3,022.9	$ 3,108.1	$ 3,022.9	$ 3,108.1