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, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		$ 29,923,912	$ 29,587,656
Fixed maturities, at fair value		30,651,790	30,256,602
Non-credit Related OTTI	[1]	(49,680)	(51,135)
Amortized cost of short-term investments, available for sale		260,407	626,142
Short-term investments, at fair value		260,153	625,193
Cost of equity securities		1,017,172	996,610
Equity securities, at fair value		1,094,509	1,037,331
Available-for-sale Securities, Amortized Cost Basis		31,201,491	31,210,408
Available for sale securities, Gross unrealized gains		1,116,635	1,078,735
Available for sale securities, Gross unrealized losses		(311,674)	(370,017)
Total investments available for sale		32,006,452	31,919,126
Excluding Life Funds Withheld Assets
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		28,182,951	27,768,929
Gross unrealized gains on Fixed maturities		562,562	540,262
Gross unrealized losses on Fixed maturities		(304,704)	(360,631)
Fixed maturities, at fair value		28,440,809	27,948,560
Non-credit Related OTTI	[1]	(49,680)	(51,135)
Amortized cost of short-term investments, available for sale		260,407	626,142
Short term investments, gross unrealized gains		208	227
Short term investments, gross unrealized losses		(462)	(1,176)
Short-term investments, at fair value		260,153	625,193
Cost of equity securities		1,017,172	996,610
Equity securities, gross unrealized gains		83,845	48,931
Equity securities, gross unrealized losses		(6,508)	(8,210)
Equity securities, at fair value		1,094,509	1,037,331
Available-for-sale Securities, Amortized Cost Basis		29,460,530	29,391,681
Available for sale securities, Gross unrealized gains		646,615	589,420
Available for sale securities, Gross unrealized losses		(311,674)	(370,017)
Total investments available for sale		29,795,471	29,611,084
Excluding Life Funds Withheld Assets | U.S. Government and Government Agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		4,175,513	3,874,038
Gross unrealized gains on Fixed maturities		53,626	53,172
Gross unrealized losses on Fixed maturities		(25,786)	(32,822)
Fixed maturities, at fair value		4,203,353	3,894,388
Non-credit Related OTTI	[1]	0	0
Excluding Life Funds Withheld Assets | US States, municipalities and political subdivisions of the States
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		2,259,820	2,399,490
Gross unrealized gains on Fixed maturities		95,624	86,041
Gross unrealized losses on Fixed maturities		(4,585)	(7,419)
Fixed maturities, at fair value		2,350,859	2,478,112
Non-credit Related OTTI	[1]	0	0
Excluding Life Funds Withheld Assets | Non-U.S. Governments
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		4,962,157	5,037,482
Gross unrealized gains on Fixed maturities		113,776	112,772
Gross unrealized losses on Fixed maturities		(96,025)	(120,122)
Fixed maturities, at fair value		4,979,908	5,030,132
Non-credit Related OTTI	[1]	0	0
Excluding Life Funds Withheld Assets | Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		10,465,866	10,055,757
Gross unrealized gains on Fixed maturities		214,671	198,082
Gross unrealized losses on Fixed maturities		(101,171)	(119,110)
Fixed maturities, at fair value		10,579,366	10,134,729
Non-credit Related OTTI	[1]	(18)	(36)
Excluding Life Funds Withheld Assets | Residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		4,370,380	4,479,722
Gross unrealized gains on Fixed maturities		65,045	71,045
Gross unrealized losses on Fixed maturities		(57,990)	(58,142)
Fixed maturities, at fair value		4,377,435	4,492,625
Non-credit Related OTTI	[1]	(46,495)	(47,879)
Excluding Life Funds Withheld Assets | Commercial mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		705,158	670,005
Gross unrealized gains on Fixed maturities		5,694	5,955
Gross unrealized losses on Fixed maturities		(10,655)	(10,774)
Fixed maturities, at fair value		700,197	665,186
Non-credit Related OTTI	[1]	(1,172)	(1,191)
Excluding Life Funds Withheld Assets | Other asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		1,244,057	1,252,435
Gross unrealized gains on Fixed maturities		14,126	13,195
Gross unrealized losses on Fixed maturities		(8,492)	(12,242)
Fixed maturities, at fair value		1,249,691	1,253,388
Non-credit Related OTTI	[1]	(1,995)	(2,029)
Life Funds Withheld Assets
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		1,740,961	1,818,727
Gross unrealized gains on Fixed maturities		470,020	489,315
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		2,210,981	2,308,042
Non-credit Related OTTI	[1]	0	0
Life Funds Withheld Assets | U.S. Government and Government Agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		8,542	8,468
Gross unrealized gains on Fixed maturities		2,190	2,109
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		10,732	10,577
Non-credit Related OTTI	[1]	0	0
Life Funds Withheld Assets | Non-U.S. Governments
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		440,648	454,695
Gross unrealized gains on Fixed maturities		147,974	169,982
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		588,622	624,677
Non-credit Related OTTI	[1]	0	0
Life Funds Withheld Assets | Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		1,116,300	1,173,670
Gross unrealized gains on Fixed maturities		279,251	280,938
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		1,395,551	1,454,608
Non-credit Related OTTI	[1]	0	0
Life Funds Withheld Assets | Residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities		19,267	19,591
Gross unrealized gains on Fixed maturities		3,071	2,789
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		22,338	22,380
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		75,554	77,762
Gross unrealized gains on Fixed maturities		18,256	16,478
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		93,810	94,240
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		80,650	84,541
Gross unrealized gains on Fixed maturities		19,278	17,019
Gross unrealized losses on Fixed maturities		0	0
Fixed maturities, at fair value		99,928	101,560
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.