Investments - Contractual maturities of available for sale securities and held to maturity income securities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Fixed Maturities - AFS
Due less than one year, amortized cost	$ 2,134,578	[1]	$ 1,939,803	[1]
Due less than one year, fair value	2,146,455	[1]	1,952,250	[1]
Due after 1 through 5 years, amortized cost	8,323,556	[1]	8,521,090	[1]
Due after 1 through 5 years, fair value	8,536,843	[1]	8,877,512	[1]
Due after 5 through 10 years, amortized cost	5,281,728	[1]	4,701,391	[1]
Due after 5 through 10 years, fair value	5,342,151	[1]	5,065,158	[1]
Due after 10 years, amortized cost	2,433,723	[1]	2,427,680	[1]
Due after 10 years, fair value	2,544,447	[1]	2,790,996	[1]
Subtotal - amortized cost	18,173,585	[1]	17,589,964	[1]
Subtotal - fair value	18,569,896	[1]	18,685,916
Mortgage and asset backed securities - amortized cost	7,842,623	[1]	8,954,842	[1]
Mortgage and asset backed securities - fair value	7,885,207	[1]	9,161,004	[1]
Amortized cost of Fixed maturities	26,016,208		26,544,806
Fixed maturities, at fair value	26,455,103		27,846,920
Fixed maturities - HTM
Due less than one year, amortized cost	51,818	[1]	36,515	[1]
Due less than one year, fair value	53,135	[1]	37,580	[1]
Due after 1 through 5 years, amortized cost	207,871	[1]	195,121	[1]
Due after 1 through 5 years, fair value	220,744	[1]	205,562	[1]
Due after 5 through 10 years, amortized cost	325,119	[1]	377,541	[1]
Due after 5 through 10 years, fair value	352,538	[1]	420,008	[1]
Due after 10 years, amortized cost	1,802,517	[1]	1,886,974	[1]
Due after 10 years, fair value	2,025,321	[1]	2,239,688	[1]
Subtotal - amortized cost	2,387,325	[1]	2,496,151	[1]
Subtotal - fair value	2,651,738	[1]	2,902,838	[1]
Mortgage and asset backed securities - amortized cost	299,669	[1]	318,296	[1]
Mortgage and asset backed securities - fair value	327,243	[1]	359,966	[1]
Fixed maturities, held to maturity	2,686,994		2,814,447
Fair value of held to maturity securities	2,978,981		3,262,804
RMBS - Agency
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	4,411,540	[1]	5,054,097	[1]
Mortgage and asset backed securities - fair value	4,446,725	[1]	5,255,493	[1]
Fixed maturities, at fair value	4,446,725		5,255,493
RMBS - Non-Agency
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	418,458	[1]	678,469	[1]
Mortgage and asset backed securities - fair value	406,402	[1]	647,733	[1]
Fixed maturities, at fair value	406,402		647,733
Fixed maturities - HTM
Mortgage and asset backed securities - amortized cost	62,925	[1]	83,205	[1]
Mortgage and asset backed securities - fair value	67,749	[1]	93,707	[1]
Fixed maturities, held to maturity	62,925		83,205
Fair value of held to maturity securities	67,749		93,707
CMBS
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	1,093,641	[1]	1,010,794	[1]
Mortgage and asset backed securities - fair value	1,129,072	[1]	1,077,251	[1]
Fixed maturities, at fair value	1,129,072		1,077,251
Fixed maturities - HTM
Mortgage and asset backed securities - amortized cost	136,193	[1]	12,751	[1]
Mortgage and asset backed securities - fair value	150,932	[1]	14,799	[1]
Fixed maturities, held to maturity	136,193		12,751
Fair value of held to maturity securities	150,932		14,799
CDO
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	753,601	[1]	784,999	[1]
Mortgage and asset backed securities - fair value	714,248	[1]	709,816	[1]
Fixed maturities, at fair value	714,248		709,816
Other asset-backed securities
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	1,165,383	[1]	1,426,483	[1]
Mortgage and asset backed securities - fair value	1,188,760	[1]	1,470,711	[1]
Fixed maturities, at fair value	1,188,760	[2]	1,470,711	[2]
Fixed maturities - HTM
Mortgage and asset backed securities - amortized cost	100,551	[1]	222,340	[1]
Mortgage and asset backed securities - fair value	108,562	[1]	251,460	[1]
Fixed maturities, held to maturity	100,551	[2]	222,340	[2]
Fair value of held to maturity securities	$ 108,562	[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 $281.4 million and $308.5 million at June 30, 2013 and December 31, 2012, respectively. These securities are reflected in the table based on their call date and have net unrealized losses of $17.2 million and $19.1 million at June 30, 2013 and December 31, 2012, respectively.

[2] Covered Bonds within Fixed maturities - AFS with an amortized cost of $523.5 million and a fair value of $550.9 million and Covered Bonds within Fixed maturities - HTM with an amortized cost of $8.0 million and a fair value of $8.2 million are included within Other asset-backed securities to align the Company's classification to market indices.