Discontinued Operations (Loss from Discontinued Operations) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues
Earned insurance premiums									$ 2,058.9	$ 1,987.3	$ 2,063.6
Other revenue									62.4	57.5	100.3
Revenues (including realized gains and losses)	689.7	589.4	652.8	578.3	626.6	574.1	489.3	627.4	2,510.2	2,317.4	2,435.7
Expenses
Loss and loss adjustment expenses									1,169.3	1,040.5	1,193.9
Insurance and reinsurance acquisition expenses									399.8	376.9	430.2
Other underwriting expenses									309.3	331.3	321.8
Total expenses	643.5	555.0	543.8	466.2	492.4	518.8	485.7	475.6	2,208.5	1,972.5	2,172.9
Net loss from discontinued operations, net of tax	(12.2)	6.7	2.6	(0.5)	(0.3)	0.4	3.9	0.5	(1.8)	(42.1)	(24.0)
(Loss) gain on sale of discontinued operations, net of tax									(1.6)	46.6	(91.0)
Discontinued Operations
Revenues
Earned insurance premiums									0.1	0.8	10.6
Other revenue									0	10.8	0
Revenues (including realized gains and losses)									0.1	11.6	10.6
Expenses
Loss and loss adjustment expenses									(0.7)	78.9	48.4
Insurance and reinsurance acquisition expenses									0.1	0	(2.1)
Other underwriting expenses									3.5	(0.2)	1.7
Total expenses									2.9	78.7	48.0
Loss from discontinued operations									(2.8)	(67.1)	(37.4)
Income tax benefit									1.0	25.0	13.4
Net loss from discontinued operations, net of tax									(1.8)	(42.1)	(24.0)
(Loss) gain on sale of discontinued operations, net of tax									(1.6)	46.6	(91.0)
Net (loss) income from discontinued operations									$ (3.4)	$ 4.5	$ (115.0)