Discontinued Operations (Assets and Liabilities Classified as Held for Sale) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets held for sale
Fixed maturity investments, at fair value	$ 4,784.3	$ 5,030.5
Insurance and reinsurance premiums receivable	547.7	518.9
Deferred tax asset	173.3	155.9
Other assets	356.1	437.4
Total assets	10,456.9	12,144.3
Liabilities held for sale
Loss and loss adjustment expense reserves	3,159.8	3,079.3	3,168.9	5,702.3
Unearned insurance premiums	955.3	901.4
Ceded reinsurance payable	105.7	71.9
Other liabilities	341.0	415.7
Total liabilities	5,917.3	7,746.9
Reinsurance recoverable on unpaid losses	483.9	428.1
Reinsurance recoverable on paid losses	23.6	25.4
Discontinued Operations
Assets held for sale
Fixed maturity investments, at fair value		236.3
Insurance and reinsurance premiums receivable		9.1
Deferred tax asset		3.3
Other assets		16.0
Total assets		1,880.1
Liabilities held for sale
Loss and loss adjustment expense reserves		1,793.1
Unearned insurance premiums		0.2
Ceded reinsurance payable		12.3
Other liabilities		74.5
Total liabilities		1,880.1
Net assets held for sale		0
Reinsurance recoverable on unpaid losses		1,604.7
Reinsurance recoverable on paid losses		$ 10.7