REINSURANCE (DETAILS) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Premiums written:
Gross									$ 4,697,041,000	$ 4,139,643,000	$ 4,096,153,000
Ceded									(768,841,000)	(802,187,000)	(676,719,000)
Net									3,928,200,000	3,337,456,000	3,419,434,000
Premiums earned:
Gross									4,459,269,000	4,141,037,000	3,973,956,000
Ceded									(752,204,000)	(725,574,000)	(658,995,000)
Net	941,911,000	945,242,000	945,873,000	874,039,000	856,049,000	862,447,000	850,603,000	846,362,000	3,707,065,000	3,415,463,000	3,314,961,000
Reinsurance receivables:
Ceded losses and loss expenses									415,000,000	396,000,000	450,000,000
Provision for unrecoverable reinsurance	$ 18,000,000				$ 16,000,000				$ 18,000,000	$ 16,000,000
Percentage of gross reinsurance recoverables collectible from reinsurers rated A- or better by A.M. Best	98.80%				98.80%				98.80%	98.80%