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	Dec. 31, 2012	Dec. 31, 2011
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	$ 26,544,806	$ 25,771,715
Gross unrealized gains of Fixed maturities	1,584,812	1,194,038
Gross Unrealized Losses Related to Changes in Fair Value	(282,698)	(775,728)
Fixed maturities, at fair value	27,846,920	26,190,025
Gross Unrealized Losses Non-credit Related OTTI	(119,076)	(186,658)
Short Term Investments
Cost or Amortized cost of Short-term investments	322,563	359,378
Short Term Investments Gross Unrealized Gains	192	519
Short Term Investments Related To Changes In Fair Value	(52)	(834)
Fair value of Short-term investments	322,703	359,063
Equity securities
Cost of equity securities	617,486	480,685
Gross unrealized gains of Equity securities	31,935	27,947
Related changes in estimated fair value of Equity securities	(62)	(40,435)
Equity securities, at fair value	649,359	468,197
Total investments - AFS
Cost or Amortized cost of total investments - AFS	27,484,855	26,611,778
Gross unrealized gains of AFS securities	1,616,939	1,222,504
Related changes in estimated fair value of securities - AFS	(282,812)	(816,997)
Total investments available for sale	28,818,982	27,017,285
OTTI included in other comprehensive income (loss) of securities - AFS	(119,076)	(186,658)
HTM securities
Cost or Amortized Cost	2,814,447	2,668,978
Gross Unrealized Gains	451,038	247,445
Gross Unrealized Losses Related Changes In Estimated Fair Value	(2,681)	(20,735)
Fair Value	3,262,804	2,895,688
US Government And Government Related [Member]
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	1,906,044	1,864,354
Gross unrealized gains of Fixed maturities	131,860	130,874
Gross Unrealized Losses Related to Changes in Fair Value	(3,287)	(4,245)
Fixed maturities, at fair value	2,034,617	1,990,983
Gross Unrealized Losses Non-credit Related OTTI	0	0
HTM securities
Cost or Amortized Cost	10,788	10,399
Gross Unrealized Gains	1,651	1,510
Gross Unrealized Losses Related Changes In Estimated Fair Value	0	0
Fair Value	12,439	11,909
Corporate
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	9,837,962	9,866,677
Gross unrealized gains of Fixed maturities	723,028	527,192
Gross Unrealized Losses Related to Changes in Fair Value	(78,990)	(285,247)
Fixed maturities, at fair value	10,482,000	10,108,622
Gross Unrealized Losses Non-credit Related OTTI	(11,453)	(51,666)
HTM securities
Cost or Amortized Cost	1,425,320	1,290,209
Gross Unrealized Gains	190,871	91,313
Gross Unrealized Losses Related Changes In Estimated Fair Value	(794)	(14,433)
Fair Value	1,615,397	1,367,089
RMBS - Agency
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	5,054,097	5,189,473
Gross unrealized gains of Fixed maturities	206,931	193,782
Gross Unrealized Losses Related to Changes in Fair Value	(5,535)	(3,849)
Fixed maturities, at fair value	5,255,493	5,379,406
Gross Unrealized Losses Non-credit Related OTTI	0	0
RMBS - Non-Agency
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	678,469	851,557
Gross unrealized gains of Fixed maturities	46,132	19,667
Gross Unrealized Losses Related to Changes in Fair Value	(76,868)	(229,409)
Fixed maturities, at fair value	647,733	641,815
Gross Unrealized Losses Non-credit Related OTTI	(93,259)	(116,542)
HTM securities
Cost or Amortized Cost	83,205	80,955
Gross Unrealized Gains	10,502	6,520
Gross Unrealized Losses Related Changes In Estimated Fair Value	0	(32)
Fair Value	93,707	87,443
CMBS
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	1,010,794	927,684
Gross unrealized gains of Fixed maturities	70,745	56,704
Gross Unrealized Losses Related to Changes in Fair Value	(4,288)	(9,553)
Fixed maturities, at fair value	1,077,251	974,835
Gross Unrealized Losses Non-credit Related OTTI	(2,962)	(7,148)
HTM securities
Cost or Amortized Cost	12,751
Gross Unrealized Gains	2,048
Gross Unrealized Losses Related Changes In Estimated Fair Value	0
Fair Value	14,799
CDO
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	784,999	843,553
Gross unrealized gains of Fixed maturities	11,973	6,624
Gross Unrealized Losses Related to Changes in Fair Value	(87,156)	(191,575)
Fixed maturities, at fair value	709,816	658,602
Gross Unrealized Losses Non-credit Related OTTI	(4,872)	(4,997)
Other asset-backed securities
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	1,426,483	1,341,309
Gross unrealized gains of Fixed maturities	59,663	30,731
Gross Unrealized Losses Related to Changes in Fair Value	(15,435)	(31,791)
Fixed maturities, at fair value	1,470,711	1,340,249
Gross Unrealized Losses Non-credit Related OTTI	(6,530)	(6,305)
HTM securities
Cost or Amortized Cost	222,340	288,741
Gross Unrealized Gains	29,287	20,875
Gross Unrealized Losses Related Changes In Estimated Fair Value	(167)	(320)
Fair Value	251,460	309,296
U.S. States and political subdivisions of the States [Member]
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	1,767,669	1,698,573
Gross unrealized gains of Fixed maturities	146,294	101,025
Gross Unrealized Losses Related to Changes in Fair Value	(2,946)	(2,220)
Fixed maturities, at fair value	1,911,017	1,797,378
Gross Unrealized Losses Non-credit Related OTTI	0	0
Non-U.S. Sovereign Government, Provincial, Supranational, and Government-Related/Supported [Member]
Fixed maturities - AFS
Cost or Amortized cost of Fixed maturities	4,078,289	3,188,535
Gross unrealized gains of Fixed maturities	188,186	127,439
Gross Unrealized Losses Related to Changes in Fair Value	(8,193)	(17,839)
Fixed maturities, at fair value	4,258,282	3,298,135
Gross Unrealized Losses Non-credit Related OTTI	0	0
HTM securities
Cost or Amortized Cost	1,060,043	998,674
Gross Unrealized Gains	216,679	127,227
Gross Unrealized Losses Related Changes In Estimated Fair Value	(1,720)	(5,950)
Fair Value	$ 1,275,002	$ 1,119,951