SCHEDULE IV - REINSURANCE (Detail) - Supplemental Schedule Of Reinsurance Premiums For Insurance Companies (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Gross Amount	$ 4,624,557		$ 4,535,626		$ 4,861,073
Ceded to Other Companies	1,509,308		1,374,243		1,628,243
Assumed from Other Companies	2,574,881		2,252,678		2,474,010
Net Amount	5,690,130		5,414,061		5,706,840
Percentage of Amount to Net	45.30%		41.60%		43.40%
Life Insurance in Force [Member]
Gross Amount	0	[1]	0	[1]	0	[1]
Ceded to Other Companies	559,676	[1]	559,674	[1]	565,048	[1]
Assumed from Other Companies	88,646,215	[1]	100,908,397	[1]	129,797,640	[1]
Net Amount	88,086,538	[1]	100,348,723	[1]	129,232,592	[1]
Percentage of Amount to Net	100.60%	[1]	100.60%	[1]	100.40%	[1]
Property, Liability and Casualty Insurance Segment [Member]
Gross Amount	4,624,557		4,535,626		4,861,073
Ceded to Other Companies	1,477,000		1,342,017		1,586,968
Assumed from Other Companies	2,179,555		1,837,528		1,877,634
Net Amount	5,327,112		5,031,137		5,151,739
Percentage of Amount to Net	40.90%		36.50%		36.40%
Life Insurance Segment [Member]
Gross Amount	0		0		0
Ceded to Other Companies	32,308		32,226		41,275
Assumed from Other Companies	395,326		415,150		596,376
Net Amount	$ 363,018		$ 382,924		$ 555,101
Percentage of Amount to Net	108.90%		108.40%		107.40%

[1] Represents the sum face value outstanding of in force life reinsurance policies.