SCHEDULE I CONSOLIDATED SUMMARY OF INVESTMENTS (Detail) - OTHER THAN INVESTMENTS IN RELATED PARTIES (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Bonds and notes:
Cost or Amortized Cost	$ 30,130,267	[1]	$ 31,348,322	[1]
Fair Value	30,871,654		31,303,588
Amount Presented in the Balance Sheet	30,671,525		31,299,458
US Government and Government Agencies and Authorities [Member]
Bonds and notes:
Cost or Amortized Cost	1,864,354	[1]	2,499,079	[1]
Fair Value	1,990,983		2,565,444
Amount Presented in the Balance Sheet	1,990,983		2,565,444
Domestic Corporate Debt Securities [Member]
Bonds and notes:
Cost or Amortized Cost	10,212,083	[1]	10,962,804	[1]
Fair Value	10,462,515		10,968,971
Amount Presented in the Balance Sheet	10,462,515		10,968,971
Residential Mortgage-Backed Securities Agency [Member]
Bonds and notes:
Cost or Amortized Cost	5,189,473	[1]	5,059,249	[1]
Fair Value	5,379,406		5,203,711
Amount Presented in the Balance Sheet	5,379,406		5,203,711
Residential Mortgage-Backed Securities Non-Agency [Member]
Bonds and notes:
Cost or Amortized Cost	851,557	[1]	1,257,474	[1]
Fair Value	641,815		1,021,823
Amount Presented in the Balance Sheet	641,815		1,021,823
Commercial Mortgage Backed Securities [Member]
Bonds and notes:
Cost or Amortized Cost	927,684	[1]	1,135,075	[1]
Fair Value	974,835		1,172,507
Amount Presented in the Balance Sheet	974,835		1,172,507
Collateralized Mortgage Obligations [Member]
Bonds and notes:
Cost or Amortized Cost	843,553	[1]	920,501	[1]
Fair Value	658,602		734,138
Amount Presented in the Balance Sheet	658,602		734,138
Other Asset Backed Securities [Member]
Bonds and notes:
Cost or Amortized Cost	995,903	[1]	979,539	[1]
Fair Value	986,356		960,532
Amount Presented in the Balance Sheet	986,356		960,532
US States and Political Subdivisions Debt Securities [Member]
Bonds and notes:
Cost or Amortized Cost	1,698,573	[1]	1,379,150	[1]
Fair Value	1,797,378		1,360,456
Amount Presented in the Balance Sheet	1,797,378		1,360,456
Non US Sovereign Government Supranational And Government Related [Member]
Bonds and notes:
Cost or Amortized Cost	3,188,535	[1]	3,129,971	[1]
Fair Value	3,298,135		3,154,523
Amount Presented in the Balance Sheet	3,298,135		3,154,523
Fixed Maturities [Member]
Bonds and notes:
Cost or Amortized Cost	25,771,715	[1]	27,322,842	[1]
Fair Value	26,190,025	[1]	27,142,105	[1]
Amount Presented in the Balance Sheet	26,190,025	[1]	27,142,105	[1]
Equity Securities, Investment Summary [Member]
Bonds and notes:
Cost or Amortized Cost	480,685	[1]	56,737	[1]
Fair Value	468,197		84,767
Amount Presented in the Balance Sheet	468,197		84,767
Short-term Investments [Member]
Bonds and notes:
Cost or Amortized Cost	359,378	[1]	450,491	[1]
Fair Value	359,063	[1]	450,681	[1]
Amount Presented in the Balance Sheet	359,063	[1]	450,681	[1]
Fixed maturities held to maturity [Member]
Bonds and notes:
Cost or Amortized Cost	2,668,978	[1]	2,728,335	[1]
Fair Value	2,895,688	[1]	2,742,626	[1]
Amount Presented in the Balance Sheet	2,668,978	[1]	2,728,335	[1]
Other Long-term Investments [Member]
Bonds and notes:
Cost or Amortized Cost	849,511	[1]	789,917	[1]
Fair Value	958,681		883,409
Amount Presented in the Balance Sheet	$ 985,262		$ 893,570

[1] Investments in fixed maturities, short-term investments and held to maturity are shown at amortized cost.