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		Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		$ 31,444,747	$ 31,517,654
Fixed maturities, at fair value		32,647,573	32,257,589
Non-credit Related OTTI	[1]	(55,423)	(57,734)
Amortized cost of short-term investments, available for sale		317,939	618,851
Short-term investments, at fair value		317,304	617,390
Cost of equity securities		831,543	834,079
Equity securities, at fair value		878,407	878,919
Available-for-sale Securities, Amortized Cost Basis		32,594,229	32,970,584
Available for sale securities, Gross unrealized gains		1,488,746	1,153,289
Available for sale securities, Gross unrealized losses		(239,691)	(369,975)
Total investments available for sale		33,843,284	33,753,898
Excluding Life Funds Withheld Assets
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		29,016,396	28,839,622
Gross unrealized gains on Fixed maturities		859,790	587,258
Gross unrealized losses on Fixed maturities		(191,970)	(322,394)
Fixed maturities, at fair value		29,684,216	29,104,486
Non-credit Related OTTI	[1]	(55,423)	(57,734)
Amortized cost of short-term investments, available for sale		317,939	618,851
Short term investments, gross unrealized gains		433	967
Short term investments, gross unrealized losses		(1,068)	(2,428)
Short-term investments, at fair value		317,304	617,390
Cost of equity securities		831,543	834,079
Equity securities, gross unrealized gains		93,517	89,993
Equity securities, gross unrealized losses		(46,653)	(45,153)
Equity securities, at fair value		878,407	878,919
Available-for-sale Securities, Amortized Cost Basis		30,165,878	30,292,552
Available for sale securities, Gross unrealized gains		953,740	678,218
Available for sale securities, Gross unrealized losses		(239,691)	(369,975)
Total investments available for sale		30,879,927	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		4,483,796	5,047,621
Gross unrealized gains on Fixed maturities		101,066	52,355
Gross unrealized losses on Fixed maturities		(7,875)	(34,339)
Fixed maturities, at fair value		4,576,987	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		4,259,838	3,697,756
Gross unrealized gains on Fixed maturities		112,260	77,776
Gross unrealized losses on Fixed maturities		(5,091)	(17,561)
Fixed maturities, at fair value		4,367,007	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		303,377	319,876
Gross unrealized gains on Fixed maturities		20,313	25,644
Gross unrealized losses on Fixed maturities		(20,847)	(16,980)
Fixed maturities, at fair value		302,843	328,540
Non-credit Related OTTI	[1]	(52,025)	(54,200)
Excluding Life Funds Withheld Assets | Commercial mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		317,886	401,713
Gross unrealized gains on Fixed maturities		10,324	7,933
Gross unrealized losses on Fixed maturities		(2,725)	(4,330)
Fixed maturities, at fair value		325,485	405,316
Non-credit Related OTTI	[1]	(1,163)	(1,182)
Excluding Life Funds Withheld Assets | Collateralized debt obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		25,845	41,679
Gross unrealized gains on Fixed maturities		2	4
Gross unrealized losses on Fixed maturities		(4,118)	(9,273)
Fixed maturities, at fair value		21,729	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		1,154,679	1,164,426
Gross unrealized gains on Fixed maturities		19,123	17,665
Gross unrealized losses on Fixed maturities		(10,904)	(13,519)
Fixed maturities, at fair value		1,162,898	1,168,572
Non-credit Related OTTI	[1]	(1,027)	(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		2,436,400	2,514,048
Gross unrealized gains on Fixed maturities		149,140	125,395
Gross unrealized losses on Fixed maturities		(793)	(7,373)
Fixed maturities, at fair value		2,584,747	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		5,442,418	5,249,148
Gross unrealized gains on Fixed maturities		161,392	100,383
Gross unrealized losses on Fixed maturities		(57,115)	(97,917)
Fixed maturities, at fair value		5,546,695	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		2,428,351	2,678,032
Gross unrealized gains on Fixed maturities		535,006	475,071
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		2,963,357	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		10,315	10,721
Gross unrealized gains on Fixed maturities		2,377	2,021
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		12,692	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		597	591
Gross unrealized gains on Fixed maturities		136	161
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		733	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		23,172	24,401
Gross unrealized gains on Fixed maturities		2,657	2,552
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		25,829	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		92,586	107,968
Gross unrealized gains on Fixed maturities		16,328	14,513
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		108,914	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		105,635	132,674
Gross unrealized gains on Fixed maturities		16,086	17,121
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		121,721	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		650,259	737,735
Gross unrealized gains on Fixed maturities		226,668	195,781
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		876,927	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		3,656,521	3,535,830
Gross unrealized gains on Fixed maturities		75,341	49,535
Gross unrealized losses on Fixed maturities		(27,547)	(23,456)
Fixed maturities, at fair value		3,704,315	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		486,901	531,016
Gross unrealized gains on Fixed maturities		60,378	67,220
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		547,279	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		6,935,636	6,867,525
Gross unrealized gains on Fixed maturities		210,829	130,568
Gross unrealized losses on Fixed maturities		(54,955)	(97,646)
Fixed maturities, at fair value		7,091,510	6,900,447
Non-credit Related OTTI	[1]	0	0
Non-Financial Services Sector | Life Funds Withheld Assets | Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		1,058,886	1,132,926
Gross unrealized gains on Fixed maturities		210,376	175,702
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		1,269,262	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.