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		Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		$ 30,389,600	$ 31,517,654
Fixed maturities, at fair value		31,858,724	32,257,589
Non-credit Related OTTI	[1]	(53,613)	(57,734)
Amortized cost of short-term investments, available for sale		446,469	618,851
Short-term investments, at fair value		444,301	617,390
Cost of equity securities		955,231	834,079
Equity securities, at fair value		1,039,793	878,919
Available-for-sale Securities, Amortized Cost Basis		31,791,300	32,970,584
Available for sale securities, Gross unrealized gains		1,772,336	1,153,289
Available for sale securities, Gross unrealized losses		(220,818)	(369,975)
Total investments available for sale		33,342,818	33,753,898
Excluding Life Funds Withheld Assets
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		28,158,843	28,839,622
Gross unrealized gains on Fixed maturities		1,052,955	587,258
Gross unrealized losses on Fixed maturities		(196,880)	(322,394)
Fixed maturities, at fair value		29,014,918	29,104,486
Non-credit Related OTTI	[1]	(53,613)	(57,734)
Amortized cost of short-term investments, available for sale		446,469	618,851
Short term investments, gross unrealized gains		1,347	967
Short term investments, gross unrealized losses		(3,515)	(2,428)
Short-term investments, at fair value		444,301	617,390
Cost of equity securities		955,231	834,079
Equity securities, gross unrealized gains		104,985	89,993
Equity securities, gross unrealized losses		(20,423)	(45,153)
Equity securities, at fair value		1,039,793	878,919
Available-for-sale Securities, Amortized Cost Basis		29,560,543	30,292,552
Available for sale securities, Gross unrealized gains		1,159,287	678,218
Available for sale securities, Gross unrealized losses		(220,818)	(369,975)
Total investments available for sale		30,499,012	30,600,795
Excluding Life Funds Withheld Assets | U.S. Government and Government - Related/Supported
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		4,006,824	5,047,621
Gross unrealized gains on Fixed maturities		130,453	52,355
Gross unrealized losses on Fixed maturities		(3,189)	(34,339)
Fixed maturities, at fair value		4,134,088	5,065,637
Non-credit Related OTTI	[1]	0	0
Excluding Life Funds Withheld Assets | RMBS - Agency
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		4,330,183	3,697,756
Gross unrealized gains on Fixed maturities		127,847	77,776
Gross unrealized losses on Fixed maturities		(2,400)	(17,561)
Fixed maturities, at fair value		4,455,630	3,757,971
Non-credit Related OTTI	[1]	0	0
Excluding Life Funds Withheld Assets | RMBS - Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		287,736	319,876
Gross unrealized gains on Fixed maturities		19,145	25,644
Gross unrealized losses on Fixed maturities		(18,066)	(16,980)
Fixed maturities, at fair value		288,815	328,540
Non-credit Related OTTI	[1]	(50,013)	(54,200)
Excluding Life Funds Withheld Assets | Commercial mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		270,546	401,713
Gross unrealized gains on Fixed maturities		10,878	7,933
Gross unrealized losses on Fixed maturities		(3,110)	(4,330)
Fixed maturities, at fair value		278,314	405,316
Non-credit Related OTTI	[1]	(1,231)	(1,182)
Excluding Life Funds Withheld Assets | Collateralized debt obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		21,437	41,679
Gross unrealized gains on Fixed maturities		3	4
Gross unrealized losses on Fixed maturities		(3,640)	(9,273)
Fixed maturities, at fair value		17,800	32,410
Non-credit Related OTTI	[1]	(1,208)	(1,208)
Excluding Life Funds Withheld Assets | Other asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		1,030,209	1,164,426
Gross unrealized gains on Fixed maturities		22,669	17,665
Gross unrealized losses on Fixed maturities		(9,400)	(13,519)
Fixed maturities, at fair value		1,043,478	1,168,572
Non-credit Related OTTI	[1]	(974)	(1,144)
Excluding Life Funds Withheld Assets | US States and political subdivisions of the States
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		2,452,935	2,514,048
Gross unrealized gains on Fixed maturities		183,357	125,395
Gross unrealized losses on Fixed maturities		(1,258)	(7,373)
Fixed maturities, at fair value		2,635,034	2,632,070
Non-credit Related OTTI	[1]	0	0
Excluding Life Funds Withheld Assets | Non-U.S. Sovereign Government, Provincial, Supranational, and Government-Related/Supported
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		5,481,374	5,249,148
Gross unrealized gains on Fixed maturities		200,030	100,383
Gross unrealized losses on Fixed maturities		(73,973)	(97,917)
Fixed maturities, at fair value		5,607,431	5,251,614
Non-credit Related OTTI	[1]	0	0
Life Funds Withheld Assets
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		2,230,757	2,678,032
Gross unrealized gains on Fixed maturities		613,049	475,071
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		2,843,806	3,153,103
Non-credit Related OTTI	[1]	0	0
Life Funds Withheld Assets | U.S. Government and Government - Related/Supported
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		9,691	10,721
Gross unrealized gains on Fixed maturities		2,808	2,021
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		12,499	12,742
Non-credit Related OTTI	[1]	0	0
Life Funds Withheld Assets | RMBS - Agency
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		545	591
Gross unrealized gains on Fixed maturities		141	161
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		686	752
Non-credit Related OTTI	[1]	0	0
Life Funds Withheld Assets | RMBS - Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		21,384	24,401
Gross unrealized gains on Fixed maturities		2,868	2,552
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		24,252	26,953
Non-credit Related OTTI	[1]	0	0
Life Funds Withheld Assets | Commercial mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		86,373	107,968
Gross unrealized gains on Fixed maturities		18,646	14,513
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		105,019	122,481
Non-credit Related OTTI	[1]	0	0
Life Funds Withheld Assets | Other asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		98,736	132,674
Gross unrealized gains on Fixed maturities		19,061	17,121
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		117,797	149,795
Non-credit Related OTTI	[1]	0	0
Life Funds Withheld Assets | Non-U.S. Sovereign Government, Provincial, Supranational, and Government-Related/Supported
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		596,382	737,735
Gross unrealized gains on Fixed maturities		254,211	195,781
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		850,593	933,516
Non-credit Related OTTI	[1]	0	0
Financial Services Sector | Excluding Life Funds Withheld Assets | Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		3,657,989	3,535,830
Gross unrealized gains on Fixed maturities		95,287	49,535
Gross unrealized losses on Fixed maturities		(27,305)	(23,456)
Fixed maturities, at fair value		3,725,971	3,561,909
Non-credit Related OTTI	[1]	0	0
Financial Services Sector | Life Funds Withheld Assets | Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		441,261	531,016
Gross unrealized gains on Fixed maturities		63,203	67,220
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		504,464	598,236
Non-credit Related OTTI	[1]	0	0
Non-Financial Services Sector | Excluding Life Funds Withheld Assets | Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		6,619,610	6,867,525
Gross unrealized gains on Fixed maturities		263,286	130,568
Gross unrealized losses on Fixed maturities		(54,539)	(97,646)
Fixed maturities, at fair value		6,828,357	6,900,447
Non-credit Related OTTI	[1]	(187)	0
Non-Financial Services Sector | Life Funds Withheld Assets | Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		976,385	1,132,926
Gross unrealized gains on Fixed maturities		252,111	175,702
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		1,228,496	1,308,628
Non-credit Related OTTI	[1]	$ 0	$ 0

[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 impairment measurement date.