LOSSES AND LOSS EXPENSES (Detail) - Analysis of paid and unpaid losses and loss expenses (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Unpaid losses and loss expenses at beginning of year	$ 20,531,607	$ 20,823,524	$ 21,650,315
Unpaid losses and loss expenses recoverable	3,649,290	3,557,391	3,964,836
Net unpaid losses and loss expenses at beginning of year	16,882,317	17,266,133	17,685,479
Increase (decrease) in net losses and loss expenses incurred in respect of losses occurring in:
Current year	4,363,258	3,584,662	3,453,577
Prior years	(284,867)	(372,862)	(284,740)
Total net incurred losses and loss expenses	4,078,391	3,211,800	3,168,837
Exchange rate effects	(130,533)	(125,107)	287,752
Less net losses and loss expenses paid in respect of losses occurring in:
Current year	589,870	442,262	439,638
Prior years	3,256,332	3,028,247	3,436,297
Total net paid losses	3,846,202	3,470,509	3,875,935
Net unpaid losses and loss expenses at end of year	16,983,973	16,882,317	17,266,133
Unpaid losses and loss expenses recoverable	3,629,928	3,649,290	3,557,391
Unpaid losses and loss expenses at end of year	$ 20,613,901	$ 20,531,607	$ 20,823,524