LOSSES AND LOSS EXPENSES (Detail) - Net (favorable) adverse prior year development by line of business relating to the Insurance segment (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense, Amount	$ (284.9)	$ (372.9)	$ (284.7)
Insurance Segment [Member] | Property Lines [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense, Amount	(8.9)	(23.5)	(50.7)
Insurance Segment [Member] | Favorable Casualty and Professional Development [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense, Amount	(47.1)	(105.2)	(41.0)
Insurance Segment [Member] | Speciality and Other Lines [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense, Amount	(20.5)	1.3	28.8
Insurance Segment [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense, Amount	$ (76.5)	$ (127.4)	$ (62.9)