Investments - Contractual maturities of available for sale securities and held to maturity income securities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Fixed Maturities - AFS
Due less than one year, amortized cost	$ 2,105,725	[1]	$ 1,939,803	[1]
Due less than one year, fair value	2,121,331	[1]	1,952,250	[1]
Due after 1 through 5 years, amortized cost	9,337,994	[1]	8,521,090	[1]
Due after 1 through 5 years, fair value	9,589,870	[1]	8,877,512	[1]
Due after 5 through 10 years, amortized cost	5,434,814	[1]	4,701,391	[1]
Due after 5 through 10 years, fair value	5,516,467	[1]	5,065,158	[1]
Due after 10 years, amortized cost	2,409,523	[1]	2,427,680	[1]
Due after 10 years, fair value	2,525,129	[1]	2,790,996	[1]
Subtotal - amortized cost	19,288,056	[1]	17,589,964	[1]
Subtotal - fair value	19,752,797	[1]	18,685,916
Mortgage and asset backed securities - amortized cost	7,484,087	[1]	8,954,842	[1]
Mortgage and asset backed securities - fair value	7,529,645	[1]	9,161,004	[1]
Amortized cost of Fixed maturities	26,772,143		26,544,806
Fixed maturities, at fair value	27,282,442		27,846,920
Fixed maturities - HTM
Due less than one year, amortized cost	68,015	[1]	36,515	[1]
Due less than one year, fair value	69,473	[1]	37,580	[1]
Due after 1 through 5 years, amortized cost	202,799	[1]	195,121	[1]
Due after 1 through 5 years, fair value	215,912	[1]	205,562	[1]
Due after 5 through 10 years, amortized cost	344,228	[1]	377,541	[1]
Due after 5 through 10 years, fair value	374,388	[1]	420,008	[1]
Due after 10 years, amortized cost	1,875,019	[1]	1,886,974	[1]
Due after 10 years, fair value	2,116,165	[1]	2,239,688	[1]
Subtotal - amortized cost	2,490,061	[1]	2,496,151	[1]
Subtotal - fair value	2,775,938	[1]	2,902,838	[1]
Mortgage and asset backed securities - amortized cost	312,050	[1]	318,296	[1]
Mortgage and asset backed securities - fair value	341,002	[1]	359,966	[1]
Fixed maturities, held to maturity	2,802,111		2,814,447
Fair value of held to maturity securities	3,116,940		3,262,804
RMBS - Agency
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	4,032,158	[1]	5,054,097	[1]
Mortgage and asset backed securities - fair value	4,069,082	[1]	5,255,493	[1]
Fixed maturities, at fair value	4,069,082		5,255,493
RMBS - Non-Agency
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	407,789	[1]	678,469	[1]
Mortgage and asset backed securities - fair value	399,399	[1]	647,733	[1]
Fixed maturities, at fair value	399,399		647,733
Fixed maturities - HTM
Mortgage and asset backed securities - amortized cost	65,542	[1]	83,205	[1]
Mortgage and asset backed securities - fair value	71,122	[1]	93,707	[1]
Fixed maturities, held to maturity	65,542		83,205
Fair value of held to maturity securities	71,122		93,707
CMBS
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	1,166,285	[1]	1,010,794	[1]
Mortgage and asset backed securities - fair value	1,197,881	[1]	1,077,251	[1]
Fixed maturities, at fair value	1,197,881		1,077,251
Fixed maturities - HTM
Mortgage and asset backed securities - amortized cost	141,884	[1]	12,751	[1]
Mortgage and asset backed securities - fair value	156,182	[1]	14,799	[1]
Fixed maturities, held to maturity	141,884		12,751
Fair value of held to maturity securities	156,182		14,799
CDO
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	754,897	[1]	784,999	[1]
Mortgage and asset backed securities - fair value	712,148	[1]	709,816	[1]
Fixed maturities, at fair value	712,148		709,816
Other asset-backed securities
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	1,122,958	[1]	1,426,483	[1]
Mortgage and asset backed securities - fair value	1,151,135	[1]	1,470,711	[1]
Fixed maturities, at fair value	1,151,135	[2]	1,470,711	[3]
Fixed maturities - HTM
Mortgage and asset backed securities - amortized cost	104,624	[1]	222,340	[1]
Mortgage and asset backed securities - fair value	113,698	[1]	251,460	[1]
Fixed maturities, held to maturity	104,624	[2]	222,340
Fair value of held to maturity securities	$ 113,698		$ 251,460

[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 $271.5 million and $308.5 million at September 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 $8.8 million and $19.1 million at September 30, 2013 and December 31, 2012, respectively.

[2] Covered Bonds within Fixed maturities - AFS with an amortized cost of $531.4 million and a fair value of $560.7 million and Covered Bonds within Fixed maturities - HTM with an amortized cost of $8.3 million and a fair value of $8.3 million are included within Other asset-backed securities to align the Company's classification to market indices.

[3] Covered Bonds within Fixed maturities - AFS with an amortized cost of $605.4 million and a fair value of $647.1 million and Covered Bonds within Fixed maturities - HTM with an amortized cost of $8.4 million