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		Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		$ 30,402,019	$ 31,517,654
Fixed maturities, at fair value		31,934,135	32,257,589
Non-credit Related OTTI	[1]	(52,115)	(57,734)
Amortized cost of short-term investments, available for sale		655,792	618,851
Short-term investments, at fair value		652,772	617,390
Cost of equity securities		968,040	834,079
Equity securities, at fair value		1,038,165	878,919
Available-for-sale Securities, Amortized Cost Basis		32,025,851	32,970,584
Available for sale securities, Gross unrealized gains		1,790,000	1,153,289
Available for sale securities, Gross unrealized losses		(190,779)	(369,975)
Total investments available for sale		33,625,072	33,753,898
Excluding Life Funds Withheld Assets
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		28,300,932	28,839,622
Gross unrealized gains on Fixed maturities		1,015,910	587,258
Gross unrealized losses on Fixed maturities		(177,019)	(322,394)
Fixed maturities, at fair value		29,139,823	29,104,486
Non-credit Related OTTI	[1]	(52,115)	(57,734)
Amortized cost of short-term investments, available for sale		655,792	618,851
Short term investments, gross unrealized gains		815	967
Short term investments, gross unrealized losses		(3,835)	(2,428)
Short-term investments, at fair value		652,772	617,390
Cost of equity securities		968,040	834,079
Equity securities, gross unrealized gains		80,050	89,993
Equity securities, gross unrealized losses		(9,925)	(45,153)
Equity securities, at fair value		1,038,165	878,919
Available-for-sale Securities, Amortized Cost Basis		29,924,764	30,292,552
Available for sale securities, Gross unrealized gains		1,096,775	678,218
Available for sale securities, Gross unrealized losses		(190,779)	(369,975)
Total investments available for sale		30,830,760	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		3,828,005	5,047,621
Gross unrealized gains on Fixed maturities		108,504	52,355
Gross unrealized losses on Fixed maturities		(3,150)	(34,339)
Fixed maturities, at fair value		3,933,359	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		4,469,725	3,697,756
Gross unrealized gains on Fixed maturities		124,185	77,776
Gross unrealized losses on Fixed maturities		(2,136)	(17,561)
Fixed maturities, at fair value		4,591,774	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		279,130	319,876
Gross unrealized gains on Fixed maturities		21,381	25,644
Gross unrealized losses on Fixed maturities		(14,584)	(16,980)
Fixed maturities, at fair value		285,927	328,540
Non-credit Related OTTI	[1]	(48,731)	(54,200)
Excluding Life Funds Withheld Assets | Commercial mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		288,544	401,713
Gross unrealized gains on Fixed maturities		10,226	7,933
Gross unrealized losses on Fixed maturities		(2,666)	(4,330)
Fixed maturities, at fair value		296,104	405,316
Non-credit Related OTTI	[1]	(1,223)	(1,182)
Excluding Life Funds Withheld Assets | Collateralized debt obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		143,783	41,679
Gross unrealized gains on Fixed maturities		175	4
Gross unrealized losses on Fixed maturities		(2,677)	(9,273)
Fixed maturities, at fair value		141,281	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		959,675	1,164,426
Gross unrealized gains on Fixed maturities		20,715	17,665
Gross unrealized losses on Fixed maturities		(7,220)	(13,519)
Fixed maturities, at fair value		973,170	1,168,572
Non-credit Related OTTI	[1]	(914)	(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		2,437,321	2,514,048
Gross unrealized gains on Fixed maturities		162,609	125,395
Gross unrealized losses on Fixed maturities		(1,076)	(7,373)
Fixed maturities, at fair value		2,598,854	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		5,513,697	5,249,148
Gross unrealized gains on Fixed maturities		207,178	100,383
Gross unrealized losses on Fixed maturities		(78,734)	(97,917)
Fixed maturities, at fair value		5,642,141	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		2,101,087	2,678,032
Gross unrealized gains on Fixed maturities		693,225	475,071
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		2,794,312	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		9,405	10,721
Gross unrealized gains on Fixed maturities		2,986	2,021
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		12,391	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		537	591
Gross unrealized gains on Fixed maturities		134	161
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		671	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		49	24,401
Gross unrealized gains on Fixed maturities		16	2,552
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		65	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		83,828	107,968
Gross unrealized gains on Fixed maturities		22,141	14,513
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		105,969	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		112,446	132,674
Gross unrealized gains on Fixed maturities		25,483	17,121
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		137,929	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		589,194	737,735
Gross unrealized gains on Fixed maturities		264,997	195,781
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		854,191	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		3,687,552	3,535,830
Gross unrealized gains on Fixed maturities		104,004	49,535
Gross unrealized losses on Fixed maturities		(13,212)	(23,456)
Fixed maturities, at fair value		3,778,344	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		417,040	531,016
Gross unrealized gains on Fixed maturities		81,034	67,220
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		498,074	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		6,693,500	6,867,525
Gross unrealized gains on Fixed maturities		256,933	130,568
Gross unrealized losses on Fixed maturities		(51,564)	(97,646)
Fixed maturities, at fair value		6,898,869	6,900,447
Non-credit Related OTTI	[1]	(39)	0
Non-Financial Services Sector | Life Funds Withheld Assets | Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		888,588	1,132,926
Gross unrealized gains on Fixed maturities		296,434	175,702
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		1,185,022	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.