SCHEDULE V VALUATION AND QUALIFYING ACCOUNTS (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reinsurance recoverable on paid losses: Allowance for reinsurance balances
VALUATION AND QUALIFYING ACCOUNTS
Balance at beginning of period	$ 29.4	$ 30.0	$ 29.5
Charged to costs and expenses	8.5	(0.4)	2.3
Deductions described	(3.9)	(0.2)	(1.8)
Balance at end of period	34.0	29.4	30.0
Property and casualty insurance and reinsurance premiums receivable: Allowance for uncollectible accounts
VALUATION AND QUALIFYING ACCOUNTS
Balance at beginning of period	3.9	6.3	7.1
Charged to costs and expenses		0.2	1.5
Charged to other accounts	(0.5)	(1.0)	(1.8)
Deductions described		(1.6)	(0.5)
Balance at end of period	$ 3.4	$ 3.9	$ 6.3