Investments - Cost (amortized cost for fixed maturities and short-term investments), fair value, gross unrealized gains, gross unrealized (losses), and OTTI recorded in AOCI (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
AFS securities
Amortized cost of fixed maturities	$ 27,370,101		$ 27,728,771
Fixed maturities, at fair value	29,110,400		29,359,034
Gross Unrealized Losses Non-credit related OTTI	(66,784)	[1]	(76,720)	[1]
Short-term investments, amortized cost	169,903		257,221
Short-term investments, at fair value	168,862		256,727
Cost of equity securities	665,682		763,833
Equity securities, at fair value	783,471		868,292
Available for sale securities, Cost or amortized cost	28,205,686		28,749,825
Available for sale securities, Gross unrealized gains	2,062,326		1,947,804
Available for sale securities, Gross unrealized losses	(205,279)		(213,576)
Total investments available for sale	30,062,733		30,484,053
Trading securities
Amortized cost of fixed maturities, trading	138,647		1,180
Fixed maturities, trading at fair value	139,377		1,171
Excluding Life Funds Withheld Assets
AFS securities
Amortized cost of fixed maturities	23,579,612		23,427,432
Gross unrealized gains on Fixed maturities	1,001,956		936,840
Gross unrealized losses on Fixed maturities	(189,147)		(186,803)
Fixed maturities, at fair value	24,392,421		24,177,469
Gross Unrealized Losses Non-credit related OTTI	(66,784)	[1]	(76,720)	[1]
Short-term investments, amortized cost	169,903		257,221
Short-term investments, gross unrealized gains	149		49
Short-term investments, gross unrealized losses	(1,190)		(543)
Short-term investments, at fair value	168,862		256,727
Cost of equity securities	665,682		763,833
Equity securities, gross unrealized gains	132,731		130,689
Equity securities, gross unrealized losses	(14,942)		(26,230)
Equity securities, at fair value	783,471		868,292
Available for sale securities, Cost or amortized cost	24,415,197		24,448,486
Available for sale securities, Gross unrealized gains	1,134,836		1,067,578
Available for sale securities, Gross unrealized losses	(205,279)		(213,576)
Total investments available for sale	25,344,754		25,302,488
Excluding Life Funds Withheld Assets | U.S. Government and Government - Related/Supported
AFS securities
Amortized cost of fixed maturities	3,299,458		2,100,851
Gross unrealized gains on Fixed maturities	87,025		77,889
Gross unrealized losses on Fixed maturities	(8,141)		(6,787)
Fixed maturities, at fair value	3,378,342		2,171,953
Gross Unrealized Losses Non-credit related OTTI	0	[1]	0	[1]
Excluding Life Funds Withheld Assets | Corporate
AFS securities
Amortized cost of fixed maturities	7,806,607	[2]	8,462,130	[3]
Gross unrealized gains on Fixed maturities	398,357	[2]	365,805	[3]
Gross unrealized losses on Fixed maturities	(50,326)	[2]	(49,562)	[3]
Fixed maturities, at fair value	8,154,638	[2]	8,778,373	[3]
Gross Unrealized Losses Non-credit related OTTI	(3,309)	[1],[2]	(3,309)	[1],[3]
Excluding Life Funds Withheld Assets | RMBS - Agency
AFS securities
Amortized cost of fixed maturities	3,585,638		3,625,171
Gross unrealized gains on Fixed maturities	131,468		114,188
Gross unrealized losses on Fixed maturities	(5,772)		(10,783)
Fixed maturities, at fair value	3,711,334		3,728,576
Gross Unrealized Losses Non-credit related OTTI	0	[1]	0	[1]
Excluding Life Funds Withheld Assets | RMBS - Non-Agency
AFS securities
Amortized cost of fixed maturities	368,317		404,398
Gross unrealized gains on Fixed maturities	29,770		41,108
Gross unrealized losses on Fixed maturities	(17,952)		(18,155)
Fixed maturities, at fair value	380,135		427,351
Gross Unrealized Losses Non-credit related OTTI	(58,364)	[1]	(67,918)	[1]
Excluding Life Funds Withheld Assets | Commercial mortgage-backed securities
AFS securities
Amortized cost of fixed maturities	1,010,518		1,033,819
Gross unrealized gains on Fixed maturities	25,603		23,987
Gross unrealized losses on Fixed maturities	(3,401)		(5,262)
Fixed maturities, at fair value	1,032,720		1,052,544
Gross Unrealized Losses Non-credit related OTTI	(1,801)	[1]	(2,033)	[1]
Excluding Life Funds Withheld Assets | Collateralized debt obligations
AFS securities
Amortized cost of fixed maturities	520,929		717,544
Gross unrealized gains on Fixed maturities	1,675		1,659
Gross unrealized losses on Fixed maturities	(21,630)		(27,169)
Fixed maturities, at fair value	500,974		692,034
Gross Unrealized Losses Non-credit related OTTI	(1,648)	[1]	(1,663)	[1]
Excluding Life Funds Withheld Assets | Other asset-backed securities
AFS securities
Amortized cost of fixed maturities	1,134,928		1,028,528
Gross unrealized gains on Fixed maturities	41,386		42,810
Gross unrealized losses on Fixed maturities	(8,947)		(6,045)
Fixed maturities, at fair value	1,167,367		1,065,293
Gross Unrealized Losses Non-credit related OTTI	(1,662)	[1]	(1,797)	[1]
Excluding Life Funds Withheld Assets | US States and political subdivisions of the States
AFS securities
Amortized cost of fixed maturities	1,842,561		1,892,566
Gross unrealized gains on Fixed maturities	131,843		129,910
Gross unrealized losses on Fixed maturities	(1,264)		(1,204)
Fixed maturities, at fair value	1,973,140		2,021,272
Gross Unrealized Losses Non-credit related OTTI	0	[1]	0	[1]
Excluding Life Funds Withheld Assets | Non-U.S. Sovereign Government, Provincial, Supranational, and Government-Related/Supported
AFS securities
Amortized cost of fixed maturities	4,010,656		4,162,425
Gross unrealized gains on Fixed maturities	154,829		139,484
Gross unrealized losses on Fixed maturities	(71,714)		(61,836)
Fixed maturities, at fair value	4,093,771		4,240,073
Gross Unrealized Losses Non-credit related OTTI	0	[1]	0	[1]
Life Funds Withheld Assets
AFS securities
Amortized cost of fixed maturities	3,790,489		4,301,339
Gross unrealized gains on Fixed maturities	927,490		880,226
Gross unrealized losses on Fixed maturities	0		0
Fixed maturities, at fair value	4,717,979		5,181,565
Gross Unrealized Losses Non-credit related OTTI	0	[1]	0	[1]
Trading securities
Amortized cost of fixed maturities, trading	138,647		1,180
Fixed maturities, trading at fair value	139,377		1,171
Life Funds Withheld Assets | U.S. Government and Government - Related/Supported
AFS securities
Amortized cost of fixed maturities	13,163		14,866
Gross unrealized gains on Fixed maturities	4,450		3,858
Gross unrealized losses on Fixed maturities	0		0
Fixed maturities, at fair value	17,613		18,724
Gross Unrealized Losses Non-credit related OTTI	0	[1]	0	[1]
Life Funds Withheld Assets | Corporate
AFS securities
Amortized cost of fixed maturities	2,277,295	[2]	2,407,849	[3]
Gross unrealized gains on Fixed maturities	468,931	[2]	410,131	[3]
Gross unrealized losses on Fixed maturities	0	[2]	0	[3]
Fixed maturities, at fair value	2,746,226	[2]	2,817,980	[3]
Gross Unrealized Losses Non-credit related OTTI	0	[1],[2]	0	[1]
Trading securities
Amortized cost of fixed maturities, trading	136,681		1,180
Fixed maturities, trading at fair value	137,438		1,171
Life Funds Withheld Assets | RMBS - Agency
AFS securities
Amortized cost of fixed maturities	1,641		3,301
Gross unrealized gains on Fixed maturities	489		481
Gross unrealized losses on Fixed maturities	0		0
Fixed maturities, at fair value	2,130		3,782
Gross Unrealized Losses Non-credit related OTTI	0	[1]	0	[1]
Life Funds Withheld Assets | RMBS - Non-Agency
AFS securities
Amortized cost of fixed maturities	32,880		71,075
Gross unrealized gains on Fixed maturities	5,928		14,260
Gross unrealized losses on Fixed maturities	0		0
Fixed maturities, at fair value	38,808		85,335
Gross Unrealized Losses Non-credit related OTTI	0	[1]	0	[1]
Life Funds Withheld Assets | Commercial mortgage-backed securities
AFS securities
Amortized cost of fixed maturities	131,830		168,886
Gross unrealized gains on Fixed maturities	27,427		24,281
Gross unrealized losses on Fixed maturities	0		0
Fixed maturities, at fair value	159,257		193,167
Gross Unrealized Losses Non-credit related OTTI	0	[1]	0	[1]
Life Funds Withheld Assets | Other asset-backed securities
AFS securities
Amortized cost of fixed maturities	209,714		238,168
Gross unrealized gains on Fixed maturities	34,426		35,373
Gross unrealized losses on Fixed maturities	0		0
Fixed maturities, at fair value	244,140		273,541
Gross Unrealized Losses Non-credit related OTTI	0	[1]	0	[1]
Trading securities
Amortized cost of fixed maturities, trading	1,966
Fixed maturities, trading at fair value	1,939
Life Funds Withheld Assets | Non-U.S. Sovereign Government, Provincial, Supranational, and Government-Related/Supported
AFS securities
Amortized cost of fixed maturities	1,123,966		1,397,194
Gross unrealized gains on Fixed maturities	385,839		391,842
Gross unrealized losses on Fixed maturities	0		0
Fixed maturities, at fair value	1,509,805		1,789,036
Gross Unrealized Losses Non-credit related OTTI	$ 0	[1]	$ 0	[1]

[1] Represents the non-credit component of OTTI losses, adjusted for subsequent sales of securities. It does not include the change in fair value subsequent to the date an impairment was recorded.

[2] Included are certain medium term notes supported primarily by pools of European investment grade credit with varying degrees of leverage. The notes have a fair value of $74.8 million and an amortized cost of $63.8 million. These notes allow the investor to participate in cash flows of the underlying bonds including certain residual values, which could serve to either decrease or increase the ultimate values of these notes.

[3] Included are certain medium term notes supported primarily by pools of European investment grade credit with varying degrees of leverage. The notes have a fair value of $79.9 million and an amortized cost of $68.4 million. These notes allow the investor to participate in cash flows of the underlying bonds including certain residual values, which could serve to either decrease or increase the ultimate values of these notes.