Investments - Contractual maturities of available for sale securities and held to maturity income securities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Fixed Maturities - AFS
Due less than one year, amortized cost	$ 2,102,831	[1]	$ 1,939,803	[1]
Due less than one year, fair value	2,118,337	[1]	1,952,250	[1]
Due after 1 through 5 years, amortized cost	8,096,248	[1]	8,521,090	[1]
Due after 1 through 5 years, fair value	8,425,698	[1]	8,877,512	[1]
Due after 5 through 10 years, amortized cost	5,136,565	[1]	4,701,391	[1]
Due after 5 through 10 years, fair value	5,459,235	[1]	5,065,158	[1]
Due after 10 years, amortized cost	2,468,528	[1]	2,427,680	[1]
Due after 10 years, fair value	2,766,729	[1]	2,790,996	[1]
Subtotal - amortized cost	17,804,172	[1]	17,589,964	[1]
Subtotal - fair value	18,769,999	[1]	18,685,916
Mortgage and asset backed securities - amortized cost	8,384,351	[1]	8,954,842	[1]
Mortgage and asset backed securities - fair value	8,579,186	[1]	9,161,004	[1]
Amortized cost of Fixed maturities	26,188,523		26,544,806
Fixed maturities, at fair value	27,349,185		27,846,920
Fixed maturities - HTM
Due less than one year, amortized cost	27,480	[1]	36,515	[1]
Due less than one year, fair value	28,862	[1]	37,580	[1]
Due after 1 through 5 years, amortized cost	176,470	[1]	195,121	[1]
Due after 1 through 5 years, fair value	186,992	[1]	205,562	[1]
Due after 5 through 10 years, amortized cost	369,716	[1]	377,541	[1]
Due after 5 through 10 years, fair value	415,524	[1]	420,008	[1]
Due after 10 years, amortized cost	1,789,892	[1]	1,886,974	[1]
Due after 10 years, fair value	2,113,183	[1]	2,239,688	[1]
Subtotal - amortized cost	2,363,558	[1]	2,496,151	[1]
Subtotal - fair value	2,744,561	[1]	2,902,838	[1]
Mortgage and asset backed securities - amortized cost	298,263	[1]	318,296	[1]
Mortgage and asset backed securities - fair value	341,817	[1]	359,966	[1]
Fixed maturities, held to maturity	2,661,821		2,814,447
Fair value of held to maturity securities	3,086,378		3,262,804
RMBS - Agency
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	4,684,803	[1]	5,054,097	[1]
Mortgage and asset backed securities - fair value	4,840,708	[1]	5,255,493	[1]
Fixed maturities, at fair value	4,840,708		5,255,493
RMBS - Non-Agency
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	600,120	[1]	678,469	[1]
Mortgage and asset backed securities - fair value	593,391	[1]	647,733	[1]
Fixed maturities, at fair value	593,391		647,733
Fixed maturities - HTM
Mortgage and asset backed securities - amortized cost	62,604	[1]	83,205	[1]
Mortgage and asset backed securities - fair value	70,675	[1]	93,707	[1]
Fixed maturities, held to maturity	62,604		83,205
Fair value of held to maturity securities	70,675		93,707
CMBS
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	1,094,389	[1]	1,010,794	[1]
Mortgage and asset backed securities - fair value	1,153,341	[1]	1,077,251	[1]
Fixed maturities, at fair value	1,153,341		1,077,251
Fixed maturities - HTM
Mortgage and asset backed securities - amortized cost	135,505	[1]	12,751	[1]
Mortgage and asset backed securities - fair value	158,218	[1]	14,799	[1]
Fixed maturities, held to maturity	135,505		12,751
Fair value of held to maturity securities	158,218		14,799
CDO
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	764,942	[1]	784,999	[1]
Mortgage and asset backed securities - fair value	711,067	[1]	709,816	[1]
Fixed maturities, at fair value	711,067		709,816
Other asset-backed securities
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	1,240,097	[1]	1,426,483	[1]
Mortgage and asset backed securities - fair value	1,280,679	[1]	1,470,711	[1]
Fixed maturities, at fair value	1,280,679	[2]	1,470,711	[2]
Fixed maturities - HTM
Mortgage and asset backed securities - amortized cost	100,154	[1]	222,340	[1]
Mortgage and asset backed securities - fair value	112,924	[1]	251,460	[1]
Fixed maturities, held to maturity	100,154	[2]	222,340	[2]
Fair value of held to maturity securities	$ 112,924	[2]	$ 251,460	[2]

[1] Included in the table above are Tier One and Upper Tier Two securities, representing committed term debt and hybrid instruments, which are senior to the common and preferred equities of the financial institutions, at their fair value of $283.5 million and $308.5 million at March 31, 2013 and December 31, 2012, respectively. These securities are reflected in the table based on their call date and have net unrealized losses of $12.1 million and $19.1 million at March 31, 2013 and December 31, 2012, respectively.

[2] Covered Bonds within Fixed maturities - AFS with an amortized cost of $485.5 million and a fair value of $521.0 million and Covered Bonds within Fixed maturities - HTM with an amortized cost of $7.9 million and a fair value of $8.1 million are included within Other asset-backed securities to align the Company's classification to market indices.