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	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	$ 25,442,779	$ 25,771,715
Gross unrealized gains of Fixed maturities	1,348,756	1,194,038
Gross Unrealized Losses Related to Changes in Fair Value	(401,150)	(589,070)
Gross Unrealized Losses Non-credit Related OTTI	(147,583)	(186,658)
Fixed maturities, at fair value	26,242,802	26,190,025
Short Term Investments
Cost or Amortized cost of Short-term investments	227,321	359,378
Short Term Investments Gross Unrealized Gains	293	519
Short Term Investments Related To Changes In Fair Value	(234)	(834)
Fair value of Short-term investments	227,380	359,063
Equity securities
Cost of equity securities	553,715	480,685
Gross unrealized gains of Equity securities	3,212	27,947
Related changes in estimated fair value of Equity securities	(27,871)	(40,435)
Equity securities, at fair value	529,056	468,197
Total investments - AFS
Cost or Amortized cost of total investments - AFS	26,223,815	26,611,778
Gross unrealized gains of AFS securities	1,352,261	1,222,504
Related changes in estimated fair value of securities - AFS	(429,255)	(630,339)
OTTI included in other comprehensive income (loss) of securities - AFS	(147,583)	(186,658)
Fair value of securities - AFS	26,999,238	27,017,285
HTM securities
Cost or Amortized Cost	2,716,357	2,668,978
Gross Unrealized Gains	303,135	247,445
Gross Unrealized Losses Related Changes In Estimated Fair Value	(12,500)	(20,735)
Fair Value	3,006,992	2,895,688
US Government And Government Related [Member]
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	1,971,384	1,864,354
Gross unrealized gains of Fixed maturities	133,040	130,874
Gross Unrealized Losses Related to Changes in Fair Value	(2,799)	(4,245)
Gross Unrealized Losses Non-credit Related OTTI	0	0
Fixed maturities, at fair value	2,101,625	1,990,983
HTM securities
Cost or Amortized Cost	10,458	10,399
Gross Unrealized Gains	1,753	1,510
Gross Unrealized Losses Related Changes In Estimated Fair Value	0	0
Fair Value	12,211	11,909
Corporate
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	9,297,657	9,866,677
Gross unrealized gains of Fixed maturities	597,211	527,192
Gross Unrealized Losses Related to Changes in Fair Value	(157,659)	(233,581)
Gross Unrealized Losses Non-credit Related OTTI	(16,056)	(51,666)
Fixed maturities, at fair value	9,721,153	10,108,622
HTM securities
Cost or Amortized Cost	1,387,033	1,290,209
Gross Unrealized Gains	131,267	91,313
Gross Unrealized Losses Related Changes In Estimated Fair Value	(8,847)	(14,433)
Fair Value	1,509,453	1,367,089
Medium-term Notes [Member]
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	199,100	297,700
Fixed maturities, at fair value	186,100	266,000
Tier One And Upper Tier Two Securities [Member]
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	420,300	494,900
Fixed maturities, at fair value	346,200	386,100
RMBS - Agency
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	5,001,023	5,189,473
Gross unrealized gains of Fixed maturities	203,766	193,782
Gross Unrealized Losses Related to Changes in Fair Value	(2,476)	(3,849)
Gross Unrealized Losses Non-credit Related OTTI	0	0
Fixed maturities, at fair value	5,202,313	5,379,406
RMBS - Non-Agency
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	728,309	851,557
Gross unrealized gains of Fixed maturities	21,822	19,667
Gross Unrealized Losses Related to Changes in Fair Value	(52,341)	(112,867)
Gross Unrealized Losses Non-credit Related OTTI	(113,247)	(116,542)
Fixed maturities, at fair value	584,543	641,815
HTM securities
Cost or Amortized Cost	81,028	80,955
Gross Unrealized Gains	6,077	6,520
Gross Unrealized Losses Related Changes In Estimated Fair Value	(15)	(32)
Fair Value	87,090	87,443
CMBS
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	842,802	927,684
Gross unrealized gains of Fixed maturities	66,058	56,704
Gross Unrealized Losses Related to Changes in Fair Value	(487)	(2,405)
Gross Unrealized Losses Non-credit Related OTTI	(3,581)	(7,148)
Fixed maturities, at fair value	904,792	974,835
HTM securities
Cost or Amortized Cost	12,546
Gross Unrealized Gains	1,667
Gross Unrealized Losses Related Changes In Estimated Fair Value	0
Fair Value	14,213
CDO
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	796,018	843,553
Gross unrealized gains of Fixed maturities	8,095	6,624
Gross Unrealized Losses Related to Changes in Fair Value	(149,211)	(186,578)
Gross Unrealized Losses Non-credit Related OTTI	(4,884)	(4,997)
Fixed maturities, at fair value	650,018	658,602
Other asset-backed securities
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	1,392,065	1,341,309
Gross unrealized gains of Fixed maturities	44,974	30,731
Gross Unrealized Losses Related to Changes in Fair Value	(19,486)	(25,486)
Gross Unrealized Losses Non-credit Related OTTI	(9,815)	(6,305)
Fixed maturities, at fair value	1,407,738	1,340,249
HTM securities
Cost or Amortized Cost	217,347	288,741
Gross Unrealized Gains	20,156	20,875
Gross Unrealized Losses Related Changes In Estimated Fair Value	(464)	(320)
Fair Value	237,039	309,296
Covered Bonds [Member]
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	478,100	345,400
Fixed maturities, at fair value	500,500	353,900
HTM securities
Cost or Amortized Cost	8,100	8,100
Fair Value	7,800	7,700
U.S. States and political subdivisions of the States [Member]
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	1,640,991	1,698,573
Gross unrealized gains of Fixed maturities	125,221	101,025
Gross Unrealized Losses Related to Changes in Fair Value	(1,781)	(2,220)
Gross Unrealized Losses Non-credit Related OTTI	0	0
Fixed maturities, at fair value	1,764,431	1,797,378
Non US Sovereign Government Supranational And Government Related [Member]
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	3,772,530	3,188,535
Gross unrealized gains of Fixed maturities	148,569	127,439
Gross Unrealized Losses Related to Changes in Fair Value	(14,910)	(17,839)
Gross Unrealized Losses Non-credit Related OTTI	0	0
Fixed maturities, at fair value	3,906,189	3,298,135
HTM securities
Cost or Amortized Cost	1,007,945	998,674
Gross Unrealized Gains	142,215	127,227
Gross Unrealized Losses Related Changes In Estimated Fair Value	(3,174)	(5,950)
Fair Value	$ 1,146,986	$ 1,119,951