Investments - Contractual maturities of available for sale securities and held to maturity income securities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Fixed Maturities - AFS
Due less than one year, amortized cost	$ 2,209,571	[1]	$ 2,052,251	[1]
Due less than one year, fair value	2,222,523	[1]	2,060,365	[1]
Due after 1 through 5 years, amortized cost	10,037,689	[1]	10,075,087	[1]
Due after 1 through 5 years, fair value	10,290,224	[1]	10,305,986	[1]
Due after 5 through 10 years, amortized cost	5,263,018	[1]	5,474,120	[1]
Due after 5 through 10 years, fair value	5,400,185	[1]	5,507,450	[1]
Due after 10 years, amortized cost	2,311,574	[1]	2,385,406	[1]
Due after 10 years, fair value	2,483,332	[1]	2,475,233	[1]
Subtotal - amortized cost	19,821,852	[1]	19,986,864	[1]
Subtotal - fair value	20,396,264	[1]	20,349,034
Mortgage and asset backed securities - amortized cost	6,663,312	[1]	7,125,010	[1]
Mortgage and asset backed securities - fair value	6,743,560	[1]	7,151,102	[1]
Amortized cost of Fixed maturities	26,485,164		27,111,874
Fixed maturities, at fair value	27,139,824		27,500,136
Fixed maturities - HTM
Due less than one year, amortized cost	67,170	[1]	65,651	[1]
Due less than one year, fair value	68,553	[1]	66,766	[1]
Due after 1 through 5 years, amortized cost	268,264	[1]	240,802	[1]
Due after 1 through 5 years, fair value	285,906	[1]	255,322	[1]
Due after 5 through 10 years, amortized cost	558,210	[1]	455,633	[1]
Due after 5 through 10 years, fair value	626,387	[1]	492,095	[1]
Due after 10 years, amortized cost	1,642,287	[1]	1,778,158	[1]
Due after 10 years, fair value	1,878,378	[1]	1,974,844	[1]
Subtotal - amortized cost	2,535,931	[1]	2,540,244	[1]
Subtotal - fair value	2,859,224	[1]	2,789,027	[1]
Mortgage and asset backed securities - amortized cost	318,556	[1]	318,451	[1]
Mortgage and asset backed securities - fair value	349,951	[1]	342,208	[1]
Fixed maturities, held to maturity	2,854,487		2,858,695
Fair value of held to maturity securities	3,209,175		3,131,235
RMBS - Agency
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	3,186,504	[1]	3,540,101	[1]
Mortgage and asset backed securities - fair value	3,222,483	[1]	3,546,122	[1]
Fixed maturities, at fair value	3,222,483		3,546,122
RMBS - Non-Agency
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	389,181	[1]	396,798	[1]
Mortgage and asset backed securities - fair value	401,393	[1]	398,768	[1]
Fixed maturities, at fair value	401,393		398,768
Fixed maturities - HTM
Mortgage and asset backed securities - amortized cost	67,037	[1]	66,987	[1]
Mortgage and asset backed securities - fair value	73,780	[1]	71,972	[1]
Fixed maturities, held to maturity	67,037		66,987
Fair value of held to maturity securities	73,780		71,972
CMBS
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	1,172,597	[1]	1,223,313	[1]
Mortgage and asset backed securities - fair value	1,198,312	[1]	1,246,795	[1]
Fixed maturities, at fair value	1,198,312		1,246,795
Fixed maturities - HTM
Mortgage and asset backed securities - amortized cost	145,005	[1]	144,924	[1]
Mortgage and asset backed securities - fair value	160,220	[1]	156,788	[1]
Fixed maturities, held to maturity	145,005		144,924
Fair value of held to maturity securities	160,220		156,788
CDO
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	758,469	[1]	754,414	[1]
Mortgage and asset backed securities - fair value	725,060	[1]	717,313	[1]
Fixed maturities, at fair value	725,060		717,313
Other asset-backed securities
Fixed Maturities - AFS
Mortgage and asset backed securities - amortized cost	1,156,561	[1]	1,210,384	[1]
Mortgage and asset backed securities - fair value	1,196,312	[1]	1,242,104	[1]
Fixed maturities, at fair value	1,196,312		1,242,104
Fixed maturities - HTM
Mortgage and asset backed securities - amortized cost	106,514	[1]	106,540	[1]
Mortgage and asset backed securities - fair value	115,951	[1]	113,448	[1]
Fixed maturities, held to maturity	106,514		106,540
Fair value of held to maturity securities	$ 115,951		$ 113,448

[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 values of $279.8 million and $282.2 million at March 31, 2014 and December 31, 2013, respectively. These securities are reflected in the table based on their call date and have net unrealized losses of $1.6 million and $4.0 million at March 31, 2014 and December 31, 2013, respectively.