Investments (Details) - Cost (amortized cost for fixed maturities and short-term investments), fair value, gross unrealized gains, gross unrealized (losses), and OTTI recorded in AOCI (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	$ 26,150,520	$ 25,771,715
Gross unrealized gains of Fixed maturities	1,666,647	1,194,038
Gross Unrealized Losses Related to Changes in Fair Value	(256,864)	(589,070)
Gross Unrealized Losses Non-credit Related OTTI	(134,010)	(186,658)
Fixed maturities, at fair value	27,426,293	26,190,025
Short Term Investments
Cost or Amortized cost of Short-term investments	323,039	359,378
Short Term Investments Gross Unrealized Gains	1,124	519
Short Term Investments Related To Changes In Fair Value	(458)	(834)
Fair value of Short-term investments	323,705	359,063
Equity securities
Cost of equity securities	554,962	480,685
Gross unrealized gains of Equity securities	16,218	27,947
Related changes in estimated fair value of Equity securities	(5,253)	(40,435)
Equity securities, at fair value	565,927	468,197
Total investments - AFS
Cost or Amortized cost of total investments - AFS	27,028,521	26,611,778
Gross unrealized gains of AFS securities	1,683,989	1,222,504
Related changes in estimated fair value of securities - AFS	(262,575)	(630,339)
OTTI included in other comprehensive income (loss) of securities - AFS	(134,010)	(186,658)
Fair value of securities - AFS	28,315,925	27,017,285
HTM securities
Cost or Amortized Cost	2,805,796	2,668,978
Gross Unrealized Gains	423,133	247,445
Gross Unrealized Losses Related Changes In Estimated Fair Value	(6,029)	(20,735)
Fair Value	3,222,900	2,895,688
US Government And Government Related [Member]
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	1,996,119	1,864,354
Gross unrealized gains of Fixed maturities	142,683	130,874
Gross Unrealized Losses Related to Changes in Fair Value	(3,434)	(4,245)
Gross Unrealized Losses Non-credit Related OTTI	0	0
Fixed maturities, at fair value	2,135,368	1,990,983
HTM securities
Cost or Amortized Cost	10,845	10,399
Gross Unrealized Gains	1,859	1,510
Gross Unrealized Losses Related Changes In Estimated Fair Value	0	0
Fair Value	12,704	11,909
Corporate
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	9,392,587	9,866,677
Gross unrealized gains of Fixed maturities	738,040	527,192
Gross Unrealized Losses Related to Changes in Fair Value	(109,187)	(233,581)
Gross Unrealized Losses Non-credit Related OTTI	(14,303)	(51,666)
Fixed maturities, at fair value	10,007,137	10,108,622
HTM securities
Cost or Amortized Cost	1,430,220	1,290,209
Gross Unrealized Gains	192,803	91,313
Gross Unrealized Losses Related Changes In Estimated Fair Value	(2,932)	(14,433)
Fair Value	1,620,091	1,367,089
RMBS - Agency
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	5,126,903	5,189,473
Gross unrealized gains of Fixed maturities	252,738	193,782
Gross Unrealized Losses Related to Changes in Fair Value	(2,738)	(3,849)
Gross Unrealized Losses Non-credit Related OTTI	0	0
Fixed maturities, at fair value	5,376,903	5,379,406
RMBS - Non-Agency
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	705,785	851,557
Gross unrealized gains of Fixed maturities	38,297	19,667
Gross Unrealized Losses Related to Changes in Fair Value	(2,716)	(112,867)
Gross Unrealized Losses Non-credit Related OTTI	(105,041)	(116,542)
Fixed maturities, at fair value	636,325	641,815
HTM securities
Cost or Amortized Cost	83,896	80,955
Gross Unrealized Gains	9,582	6,520
Gross Unrealized Losses Related Changes In Estimated Fair Value	0	(32)
Fair Value	93,478	87,443
CMBS
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	963,365	927,684
Gross unrealized gains of Fixed maturities	75,031	56,704
Gross Unrealized Losses Related to Changes in Fair Value	(1,123)	(2,405)
Gross Unrealized Losses Non-credit Related OTTI	(2,864)	(7,148)
Fixed maturities, at fair value	1,034,409	974,835
HTM securities
Cost or Amortized Cost	12,917
Gross Unrealized Gains	2,109
Gross Unrealized Losses Related Changes In Estimated Fair Value	0
Fair Value	15,026
CDO
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	791,737	843,553
Gross unrealized gains of Fixed maturities	9,735	6,624
Gross Unrealized Losses Related to Changes in Fair Value	(114,017)	(186,578)
Gross Unrealized Losses Non-credit Related OTTI	(4,889)	(4,997)
Fixed maturities, at fair value	682,566	658,602
Other asset-backed securities
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	1,421,005	1,341,309
Gross unrealized gains of Fixed maturities	57,025	30,731
Gross Unrealized Losses Related to Changes in Fair Value	(12,573)	(25,486)
Gross Unrealized Losses Non-credit Related OTTI	(6,913)	(6,305)
Fixed maturities, at fair value	1,458,544	1,340,249
HTM securities
Cost or Amortized Cost	224,508	288,741
Gross Unrealized Gains	29,218	20,875
Gross Unrealized Losses Related Changes In Estimated Fair Value	(295)	(320)
Fair Value	253,431	309,296
U.S. States and political subdivisions of the States [Member]
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	1,665,392	1,698,573
Gross unrealized gains of Fixed maturities	156,366	101,025
Gross Unrealized Losses Related to Changes in Fair Value	(1,653)	(2,220)
Gross Unrealized Losses Non-credit Related OTTI	0	0
Fixed maturities, at fair value	1,820,105	1,797,378
Non-U.S. Sovereign Government, Provincial, Supranational, and Government-Related/Supported [Member]
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	4,087,627	3,188,535
Gross unrealized gains of Fixed maturities	196,732	127,439
Gross Unrealized Losses Related to Changes in Fair Value	(9,423)	(17,839)
Gross Unrealized Losses Non-credit Related OTTI	0	0
Fixed maturities, at fair value	4,274,936	3,298,135
HTM securities
Cost or Amortized Cost	1,043,410	998,674
Gross Unrealized Gains	187,562	127,227
Gross Unrealized Losses Related Changes In Estimated Fair Value	(2,802)	(5,950)
Fair Value	$ 1,228,170	$ 1,119,951