Discontinued Operations (Assets and Liabilities Classified as Held for Sale) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Assets held for sale
Fixed maturity investments, at fair value	$ 5,030.5	$ 5,196.2
Cash	382.8	462.4
Insurance and reinsurance premiums receivable	518.9	556.3
Deferred acquisition costs	174.7	195.3
Deferred tax asset	155.9	228.3
Other assets	458.1	503.0
Total assets	12,144.3	12,895.4
Liabilities held for sale
Loss and loss adjustment expense reserves	3,079.3	3,168.9	5,702.3	5,736.8
Unearned insurance premiums	901.4	924.1
Ceded reinsurance payable	71.9	116.5
Other liabilities	362.9	452.8
Total liabilities	7,746.9	8,637.2
Reinsurance recoverable on unpaid losses	428.1	429.1
Reinsurance recoverable on paid losses	25.4	17.9
Discontinued Operations
Assets held for sale
Fixed maturity investments, at fair value	236.3	338.1
Cash	0	0
Insurance and reinsurance premiums receivable	9.1	11.0
Deferred acquisition costs	0	0
Deferred tax asset	3.3	5.1
Other assets	16.0	16.2
Total assets	1,880.1	2,226.8
Liabilities held for sale
Loss and loss adjustment expense reserves	1,793.1	2,052.6
Unearned insurance premiums	0.2	0.5
Ceded reinsurance payable	12.3	21.9
Other liabilities	74.5	151.8
Total liabilities	1,880.1	2,226.8
Net assets held for sale	0	0
Reinsurance recoverable on unpaid losses	1,604.7	1,840.8
Reinsurance recoverable on paid losses		$ 15.6