Discontinued Operations (Net Assets Held for Sale) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Assets held for sale
Fixed maturity investments, at fair value	$ 4,988.7	$ 5,030.5
Reinsurance recoverable on unpaid losses	425.2	428.1
Reinsurance recoverable on paid losses	15.2	25.4
Insurance and reinsurance premiums receivable	734.8	518.9
Other assets	537.7	458.1
Total assets	12,416.4	12,144.3
Liabilities held for sale
Loss and loss adjustment expense reserves	3,048.4	3,079.3	3,100.6	3,168.9
Unearned insurance premiums	1,116.6	901.4
Ceded reinsurance payable	157.9	71.9
Other liabilities	343.3	362.9
Total liabilities	7,888.5	7,746.9
Segment, Discontinued Operations
Assets held for sale
Fixed maturity investments, at fair value	222.2	236.3
Reinsurance recoverable on unpaid losses	1,540.0	1,604.7
Reinsurance recoverable on paid losses	9.5	10.7
Insurance and reinsurance premiums receivable	12.8	9.1
Deferred tax asset	3.2	3.3
Other assets	15.4	16.0
Total assets	1,803.1	1,880.1
Liabilities held for sale
Loss and loss adjustment expense reserves	1,717.3	1,793.1
Unearned insurance premiums	0.2	0.2
Ceded reinsurance payable	12.1	12.3
Other liabilities	73.5	74.5
Total liabilities	1,803.1	1,880.1
Net assets held for sale	$ 0	$ 0