Loss and Loss Adjustment Expense Reserves (Loss and Loss Adjustment Expense) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Loss and Loss Adjustment Expense Reserve
Gross beginning balance	$ 3,079.3	$ 3,168.9
Less beginning reinsurance recoverable on unpaid losses	(428.1)	(429.1)
Net loss and LAE reserves	2,651.2	2,739.8
Loss and LAE reserves acquired	0	21.3
Loss and LAE reserves consolidated — SSIE	13.6	0
Loss and LAE incurred relating to current year losses	240.5	242.9
Net favorable and unfavorable loss reserve development	11.2	1.4
Total incurred losses and LAE	229.3	244.3
Accretion of fair value adjustment to net loss and LAE reserves	0.2	1.2
Foreign currency translation adjustment to net loss and LAE reserves	1.8	(9.6)
Current year losses	(35.0)	(36.6)
Prior year losses	(237.9)	(270.6)
Total loss and LAE payments	(272.9)	(307.2)
Net loss and LAE reserves	2,623.2	2,689.8
Reinsurance recoverable on unpaid losses	425.2	410.8
Gross ending balance	$ 3,048.4	$ 3,100.6