Discontinued Operations (Net Assets Held for Sale) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Assets held for sale
Fixed maturity investments, at fair value	$ 4,931.9		$ 5,196.2
Cash	348.3		462.4
Reinsurance recoverable on unpaid losses	388.6	410.8	429.1	2,369.4	2,465.4	2,507.3
Reinsurance recoverable on paid losses	16.1		17.9
Insurance premiums receivable	706.7		556.3
Deferred acquisition costs	180.6		195.3
Deferred tax asset	540.5		569.6
Other assets	483.3		503.0
Total assets	12,283.7		12,895.4
Liabilities held for sale
Loss and loss adjustment expense reserves	3,057.9	3,100.6	3,168.9	5,329.8	5,510.8	5,702.3
Unearned insurance premiums	1,015.0		924.1
Ceded reinsurance payable	156.9		116.5
Other liabilities	371.5		452.8
Total liabilities	8,093.3		8,637.2
Segment, Discontinued Operations
Assets held for sale
Fixed maturity investments, at fair value	260.8		338.1
Cash	0		0
Reinsurance recoverable on unpaid losses	1,736.3		1,840.8
Reinsurance recoverable on paid losses	21.4		15.6
Insurance premiums receivable	9.8		11.0
Deferred acquisition costs	0		0
Deferred tax asset	3.5		5.1
Other assets	15.2		16.2
Total assets	2,047.0		2,226.8
Liabilities held for sale
Loss and loss adjustment expense reserves	1,884.2		2,052.6
Unearned insurance premiums	0.4		0.5
Ceded reinsurance payable	14.3		21.9
Other liabilities	148.1		151.8
Total liabilities	2,047.0		2,226.8
Net assets held for sale	$ 0		$ 0