Discontinued Operations (Net Assets Held for Sale) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Assets held for sale
Fixed maturity investments, at fair value	$ 4,914.0		$ 5,196.2
Cash	411.0		462.4
Reinsurance recoverable on unpaid losses	416.0		429.1
Reinsurance recoverable on paid losses	18.8		17.9
Insurance premiums receivable	684.9		556.3
Deferred acquisition costs	188.2		195.3
Deferred tax asset	555.5		569.6
Other assets	397.3		503.0
Total assets	12,307.5		12,895.4
Liabilities held for sale
Loss and loss adjustment expense reserves	3,108.1	3,057.9	3,168.9	3,059.8	5,329.8	5,702.3
Unearned insurance premiums	1,010.3		924.1
Ceded reinsurance payable	153.6		116.5
Other liabilities	362.7		452.8
Total liabilities	8,020.3		8,637.2
Segment, Discontinued Operations
Assets held for sale
Fixed maturity investments, at fair value	239.7		338.1
Reinsurance recoverable on unpaid losses	1,666.5		1,840.8
Reinsurance recoverable on paid losses	21.8		15.6
Insurance premiums receivable	9.8		11.0
Deferred tax asset	3.2		5.1
Other assets	16.2		16.2
Total assets	1,957.2		2,226.8
Liabilities held for sale
Loss and loss adjustment expense reserves	1,797.1		2,052.6
Unearned insurance premiums	0.2		0.5
Ceded reinsurance payable	12.8		21.9
Other liabilities	147.1		151.8
Total liabilities	1,957.2		2,226.8
Net assets held for sale	$ 0		$ 0