Schedule I - Consolidated Summary of Investments - other than Investments in Related Parties (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	$ 32,278,550	[1]	$ 31,339,033	[1]
Fair Value	33,295,278		33,283,356
Amount Presented in the Balance Sheet	33,019,986		32,853,308
Fixed maturities
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	27,111,874	[1]	26,544,806	[1]
Fair Value	27,500,136		27,846,920
Amount Presented in the Balance Sheet	27,500,136		27,846,920
U.S. Government and Government - Related/Supported [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	2,484,193	[1]	1,906,044	[1]
Fair Value	2,501,851		2,034,617
Amount Presented in the Balance Sheet	2,501,851		2,034,617
Corporate
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	10,802,332	[1]	9,837,962	[1]
Fair Value	11,125,830		10,482,000
Amount Presented in the Balance Sheet	11,125,830		10,482,000
Residential mortgage-backed securities - Agency ('RMBS - Agency') [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	3,540,101	[1]	5,054,097	[1]
Fair Value	3,546,122		5,255,493
Amount Presented in the Balance Sheet	3,546,122		5,255,493
Residential mortgage-backed securities - Non-Agency ('RMBS - Non-Agency') [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	396,798	[1]	678,469	[1]
Fair Value	398,768		647,733
Amount Presented in the Balance Sheet	398,768		647,733
Commercial mortgage-backed securities ('CMBS') [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	1,223,313	[1]	1,010,794	[1]
Fair Value	1,246,795		1,077,251
Amount Presented in the Balance Sheet	1,246,795		1,077,251
Collateralized debt obligations ('CDO') [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	754,414	[1]	784,999	[1]
Fair Value	717,313		709,816
Amount Presented in the Balance Sheet	717,313		709,816
Other asset-backed securities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	1,210,384	[1]	1,426,483	[1]
Fair Value	1,242,104		1,470,711
Amount Presented in the Balance Sheet	1,242,104		1,470,711
U.S. States and political subdivisions of the States [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	1,821,499	[1]	1,767,669	[1]
Fair Value	1,845,812		1,911,017
Amount Presented in the Balance Sheet	1,845,812		1,911,017
Non-U.S. Sovereign Government, Provincial, Supranational, and Government-Related/Supported [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	4,878,840	[1]	4,078,289	[1]
Fair Value	4,875,541		4,258,282
Amount Presented in the Balance Sheet	4,875,541		4,258,282
Equity securities
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	903,201	[1]	617,486	[1]
Fair Value	1,040,237		649,359
Amount Presented in the Balance Sheet	1,040,237		649,359
Short-term investments
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	455,470	[1]	322,563	[1]
Fair Value	456,288		322,703
Amount Presented in the Balance Sheet	456,288		322,703
Fixed maturities, held to maturity
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	2,858,695	[1]	2,814,447	[1]
Fair Value	3,131,235		3,262,804
Amount Presented in the Balance Sheet	2,858,695		2,814,447
Other investments
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or Amortized Cost	949,310	[1]	1,039,731	[1]
Fair Value	1,167,382		1,201,570
Amount Presented in the Balance Sheet	$ 1,164,630		$ 1,219,879

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