Supplementary Insurance Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Premium Revenue	$ 8,669,854	$ 8,254,027	$ 7,906,596
Supplementary Insurance Information, Net Investment Income	1,713,691	1,699,865	1,436,206
Supplementary Insurance Information, Benefits, Claims, Losses and Settlement Expense	(7,857,672)	(7,780,846)	(7,045,914)
Supplementary Insurance Information, Amortization of Deferred Policy Acquisition Costs	(979,365)	(912,803)	(1,003,057)
Supplementary Insurance Information, Other Operating Expense	(1,058,624)	(989,450)	(872,717)
US Traditional Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Premium Revenue	4,725,505	4,563,490	4,342,838
Supplementary Insurance Information, Net Investment Income	552,805	543,824	536,438
Supplementary Insurance Information, Benefits, Claims, Losses and Settlement Expense	(4,181,492)	(4,016,453)	(3,815,551)
Supplementary Insurance Information, Amortization of Deferred Policy Acquisition Costs	(467,067)	(471,726)	(461,164)
Supplementary Insurance Information, Other Operating Expense	(283,064)	(250,175)	(230,926)
US Non-Traditional Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Premium Revenue	20,079	22,521	14,095
Supplementary Insurance Information, Net Investment Income	644,285	721,282	498,499
Supplementary Insurance Information, Benefits, Claims, Losses and Settlement Expense	(402,387)	(443,393)	(335,581)
Supplementary Insurance Information, Amortization of Deferred Policy Acquisition Costs	(203,605)	(185,396)	(193,492)
Supplementary Insurance Information, Other Operating Expense	(105,207)	(88,380)	(78,731)
Canada Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Premium Revenue	974,581	962,311	915,764
Supplementary Insurance Information, Net Investment Income	196,205	204,851	190,337
Supplementary Insurance Information, Benefits, Claims, Losses and Settlement Expense	(804,586)	(758,565)	(706,744)
Supplementary Insurance Information, Amortization of Deferred Policy Acquisition Costs	(190,164)	(178,566)	(167,614)
Supplementary Insurance Information, Other Operating Expense	(85,415)	(83,569)	(78,935)
Europe And South Africa Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Premium Revenue	1,373,969	1,220,743	1,215,166
Supplementary Insurance Information, Net Investment Income	107,129	52,034	42,545
Supplementary Insurance Information, Benefits, Claims, Losses and Settlement Expense	(1,217,441)	(1,072,961)	(1,055,064)
Supplementary Insurance Information, Amortization of Deferred Policy Acquisition Costs	(43,549)	(40,780)	(49,732)
Supplementary Insurance Information, Other Operating Expense	(135,215)	(116,718)	(109,183)
Asia Pacific Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Premium Revenue	1,574,940	1,485,205	1,409,568
Supplementary Insurance Information, Net Investment Income	102,461	94,330	85,569
Supplementary Insurance Information, Benefits, Claims, Losses and Settlement Expense	(1,250,962)	(1,488,667)	(1,132,998)
Supplementary Insurance Information, Amortization of Deferred Policy Acquisition Costs	(74,980)	(36,335)	(131,055)
Supplementary Insurance Information, Other Operating Expense	(328,481)	(312,289)	(241,258)
Corporate And Other Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Premium Revenue	780	(243)	9,165
Supplementary Insurance Information, Net Investment Income	110,806	83,544	82,818
Supplementary Insurance Information, Benefits, Claims, Losses and Settlement Expense	(804)	(807)	24
Supplementary Insurance Information, Amortization of Deferred Policy Acquisition Costs	0	0	0
Supplementary Insurance Information, Other Operating Expense	(121,242)	(138,319)	(133,684)
Reinsurance Assumed [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Deferred Policy Acquisition Costs	3,391,291	3,573,054
Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves	27,068,134	24,814,333
Supplementary Insurance Information, Other Policy Claims and Benefits Payable	3,824,069	3,571,761
Reinsurance Assumed [Member] | US Traditional Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Deferred Policy Acquisition Costs	1,717,512	1,628,215
Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves	8,440,882	7,567,342
Supplementary Insurance Information, Other Policy Claims and Benefits Payable	1,459,444	1,285,467
Reinsurance Assumed [Member] | US Non-Traditional Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Deferred Policy Acquisition Costs	690,698	884,377
Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves	10,915,471	11,240,138
Supplementary Insurance Information, Other Policy Claims and Benefits Payable	14,656	16,045
Reinsurance Assumed [Member] | Canada Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Deferred Policy Acquisition Costs	237,738	259,575
Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves	2,861,052	2,963,561
Supplementary Insurance Information, Other Policy Claims and Benefits Payable	209,743	206,245
Reinsurance Assumed [Member] | Europe And South Africa Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Deferred Policy Acquisition Costs	279,672	301,999
Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves	2,972,346	1,050,066
Supplementary Insurance Information, Other Policy Claims and Benefits Payable	784,421	763,118
Reinsurance Assumed [Member] | Asia Pacific Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Deferred Policy Acquisition Costs	465,671	498,888
Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves	1,578,776	1,693,381
Supplementary Insurance Information, Other Policy Claims and Benefits Payable	1,344,250	1,288,016
Reinsurance Assumed [Member] | Corporate And Other Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Deferred Policy Acquisition Costs	0	0
Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves	299,607	299,845
Supplementary Insurance Information, Other Policy Claims and Benefits Payable	11,555	12,870
Reinsurance Ceded [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Deferred Policy Acquisition Costs	(48,716)	(55,258)
Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves	(602,265)	(583,620)
Supplementary Insurance Information, Other Policy Claims and Benefits Payable	(260,155)	(143,309)
Reinsurance Ceded [Member] | US Traditional Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Deferred Policy Acquisition Costs	(28,685)	(30,523)
Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves	(283,184)	(245,430)
Supplementary Insurance Information, Other Policy Claims and Benefits Payable	(194,167)	(73,994)
Reinsurance Ceded [Member] | US Non-Traditional Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Deferred Policy Acquisition Costs	0	0
Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves	0	0
Supplementary Insurance Information, Other Policy Claims and Benefits Payable	0	0
Reinsurance Ceded [Member] | Canada Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Deferred Policy Acquisition Costs	(443)	(483)
Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves	(221,537)	(233,735)
Supplementary Insurance Information, Other Policy Claims and Benefits Payable	(14,095)	(8,952)
Reinsurance Ceded [Member] | Europe And South Africa Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Deferred Policy Acquisition Costs	(7,656)	(9,492)
Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves	(35,439)	(35,515)
Supplementary Insurance Information, Other Policy Claims and Benefits Payable	(28,134)	(33,337)
Reinsurance Ceded [Member] | Asia Pacific Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Deferred Policy Acquisition Costs	(11,932)	(14,760)
Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves	(62,105)	(68,940)
Supplementary Insurance Information, Other Policy Claims and Benefits Payable	(23,631)	(26,836)
Reinsurance Ceded [Member] | Corporate And Other Segment Reporting Information [Member]
Supplementary Insurance Information, by Segment [Line Items]
Supplementary Insurance Information, Deferred Policy Acquisition Costs	0	0
Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves	0	0
Supplementary Insurance Information, Other Policy Claims and Benefits Payable	$ (128)	$ (190)