INVESTMENTS (Detail) - Analysis of continual unrealized loss position (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Fixed maturities – HTM:
Less than 12 months Fair Value	$ 244,193		$ 1,212,106
Less than 12 month Gross Unrealized Losses	(9,322)		(24,691)	[1]
Equal to or greater than 12 months Fair Value	81,779		0
Equal to or greater than 12 months Gross Unrealized Losses	(11,413)	[1]	0	[1]
US Government And Government Related [Member]
Fixed maturities – HTM:
Less than 12 months Fair Value	0		1,755
Less than 12 month Gross Unrealized Losses	0		(9)	[1]
Equal to or greater than 12 months Fair Value	0		0
Equal to or greater than 12 months Gross Unrealized Losses	0	[1]	0	[1]
Corporate Debt Securities [Member]
Fixed maturities – HTM:
Less than 12 months Fair Value	155,579		764,397
Less than 12 month Gross Unrealized Losses	(8,084)		(16,325)	[1]
Equal to or greater than 12 months Fair Value	62,343		0
Equal to or greater than 12 months Gross Unrealized Losses	(6,663)	[1]	0	[1]
Residential Mortgage-Backed Securities Non-Agency [Member]
Fixed maturities – HTM:
Less than 12 months Fair Value	9,372
Less than 12 month Gross Unrealized Losses	(32)
Equal to or greater than 12 months Fair Value	0
Equal to or greater than 12 months Gross Unrealized Losses	0	[1]
Other Asset Backed Securities [Member]
Fixed maturities – HTM:
Less than 12 months Fair Value	0		232,673
Less than 12 month Gross Unrealized Losses	0		(1,410)	[1]
Equal to or greater than 12 months Fair Value	1,106		0
Equal to or greater than 12 months Gross Unrealized Losses	(6)	[1]	0	[1]
Non US Sovereign Government Supranational And Government Related [Member]
Fixed maturities – HTM:
Less than 12 months Fair Value	79,242		175,382
Less than 12 month Gross Unrealized Losses	(1,206)		(6,401)	[1]
Equal to or greater than 12 months Fair Value	18,330		0
Equal to or greater than 12 months Gross Unrealized Losses	(4,744)	[1]	0	[1]
Residential Mortgage-Backed Securities Agency [Member]
Fixed maturities – HTM:
Less than 12 months Fair Value			37,899
Less than 12 month Gross Unrealized Losses			(546)	[1]
Equal to or greater than 12 months Fair Value			0
Equal to or greater than 12 months Gross Unrealized Losses			0	[1]
US Government And Government Related [Member]
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	289,260		307,082
Less than 12 month Gross Unrealized Losses	(332)		(25,482)	[1]
Equal to or greater than 12 months Fair Value	43,622		117,394
Equal to or greater than 12 months Gross Unrealized Losses	(3,984)	[1]	(10,417)	[1]
Corporate Debt Securities [Member]
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	1,108,177	[2],[3]	2,271,887	[4],[5]
Less than 12 month Gross Unrealized Losses	(42,978)	[2],[3]	(80,276)	[1],[4],[5]
Equal to or greater than 12 months Fair Value	1,200,717	[2],[3]	1,627,083	[4],[5]
Equal to or greater than 12 months Gross Unrealized Losses	(246,566)	[1],[2],[3]	(275,023)	[1],[4],[5]
Residential Mortgage-Backed Securities Agency [Member]
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	310,318		280,390
Less than 12 month Gross Unrealized Losses	(849)		(6,736)	[1]
Equal to or greater than 12 months Fair Value	36,960		34,186
Equal to or greater than 12 months Gross Unrealized Losses	(3,000)	[1]	(1,913)	[1]
Residential Mortgage-Backed Securities Non-Agency [Member]
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	106,294		40,052
Less than 12 month Gross Unrealized Losses	(31,714)		(2,574)	[1]
Equal to or greater than 12 months Fair Value	449,138		843,168
Equal to or greater than 12 months Gross Unrealized Losses	(197,695)	[1]	(259,715)	[1]
Commercial Mortgage Backed Securities [Member]
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	69,109		46,419
Less than 12 month Gross Unrealized Losses	(2,716)		(2,472)	[1]
Equal to or greater than 12 months Fair Value	39,444		69,475
Equal to or greater than 12 months Gross Unrealized Losses	(6,837)	[1]	(15,967)	[1]
Collateralized Debt Obligations [Member]
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	3,357		2,500
Less than 12 month Gross Unrealized Losses	(2,261)		(51)	[1]
Equal to or greater than 12 months Fair Value	636,362		715,295
Equal to or greater than 12 months Gross Unrealized Losses	(189,456)	[1]	(197,535)	[1]
Other Asset Backed Securities [Member]
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	197,585		122,548
Less than 12 month Gross Unrealized Losses	(2,497)		(1,619)	[1]
Equal to or greater than 12 months Fair Value	146,130		226,946
Equal to or greater than 12 months Gross Unrealized Losses	(25,584)	[1]	(33,546)	[1]
US States and Political Subdivisions Debt Securities [Member]
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	25,309		734,893
Less than 12 month Gross Unrealized Losses	(199)		(30,033)	[1]
Equal to or greater than 12 months Fair Value	27,646		40,907
Equal to or greater than 12 months Gross Unrealized Losses	(2,021)	[1]	(5,452)	[1]
Non US Sovereign Government Supranational And Government Related [Member]
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	265,766		459,686
Less than 12 month Gross Unrealized Losses	(4,707)		(5,116)	[1]
Equal to or greater than 12 months Fair Value	202,890		418,322
Equal to or greater than 12 months Gross Unrealized Losses	(13,166)	[1]	(40,837)	[1]
Total Fixed Maturities And Short Term Investments Available For Sale [Member]
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	2,375,175		4,265,457
Less than 12 month Gross Unrealized Losses	(88,253)		(154,359)	[1]
Equal to or greater than 12 months Fair Value	2,782,909		4,092,776
Equal to or greater than 12 months Gross Unrealized Losses	(688,309)	[1]	(840,405)	[1]
Equity Securities [Member]
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	361,585	[6]	158
Less than 12 month Gross Unrealized Losses	(40,435)	[6]	(53)	[1]
Equal to or greater than 12 months Fair Value	0	[6]	0
Equal to or greater than 12 months Gross Unrealized Losses	$ 0	[1],[6]	$ 0	[1]

[1] On securities impacted by the April 1, 2009 changes to OTTI values, length of time of impairment is measured from the point at which securities returned to a net unrealized loss position (i.e. from April 1, 2009).

[2] Included within Corporate are certain medium term notes supported primarily by pools of European investment grade credit with varying degrees of leverage. The notes, which are in a gross unrealized loss position, have a fair value of $266.0 million and an amortized cost of $297.7 million. These notes allow the investor to participate in cash flows of the underlying bonds including certain residual values, which could serve to either decrease or increase the ultimate values of these notes.

[3] Included within Corporate are Tier One and Upper Tier Two securities, representing committed term debt and hybrid instruments, which are senior to the common and preferred equities of the financial institutions. These securities, which are in a gross unrealized loss position, have a fair value of $386.1 million and an amortized cost of $494.9 million at December 31, 2011.

[4] Included within Corporate are certain medium term notes supported primarily by pools of European credit with varying degrees of leverage. The notes have a fair value of $370.8 million and an amortized cost of $423.9 million. These notes allow the investor to participate in cash flows of the underlying bonds including certain residual values, which could serve to either decrease or increase the ultimate values of these notes.

[5] Included within Corporate are Tier One and Upper Tier Two securities, representing committed term debt and hybrid instruments senior to the common and preferred equities of the financial institutions. These securities have a fair value of $757.8 million and an amortized cost of $883.0 million at December 31, 2010.

[6] Included within equity securities are investments in fixed income funds with a fair value of $91.6 million and an amortized cost of $100.0 million at December 31, 2011.