Income Taxes (Reconciliation Of The Difference Between The Provision For Income Taxes And The Expected Tax Provision At The Weighted Average Tax Rate) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Taxes [Line Items]
Underwriting gain (loss)									$ 886,615	$ 738,608	$ 259,003
Net investment income	134,046	142,143	131,224	123,157	126,127	127,872	148,729	145,781	530,570	548,509	600,202
Net realized capital gains (losses)	13,352	(9,448)	59,016	21,126	94,629	44,958	33,905	126,735	84,046	300,227	164,400
Net derivative gain (loss)									(11,599)	44,044	(9,738)
Corporate expenses									(23,421)	(24,817)	(23,976)
Interest, fee and bond issue cost amortization expense									(38,533)	(46,118)	(53,683)
Other income (expense)									18,437	(5,487)	3,318
INCOME (LOSS) BEFORE TAXES									1,446,115	1,554,966	939,526
Increase (decrease) in taxes resulting from: Other											(17,520)
Total income tax expense (benefit)									187,652	289,706	110,572
U.S. [Member]
Income Taxes [Line Items]
Underwriting gain (loss)									228,194	246,699	42,775
Net investment income									260,501	274,920	287,382
Net realized capital gains (losses)									78,006	295,814	143,326
Corporate expenses									(7,252)	(8,262)	(8,764)
Interest, fee and bond issue cost amortization expense									(37,970)	(45,452)	(50,746)
Other income (expense)									(1,561)	(7,086)	18,360
INCOME (LOSS) BEFORE TAXES									519,918	756,633	432,332
Expected tax provision at the applicable statutory rate(s)									181,972	264,822	151,316
Increase (decrease) in tax resulting from: Tax exempt income									(12,231)	(15,038)	(20,623)
Increase (decrease) in tax resulting from: Dividend received deduction									(5,910)	(7,809)	(8,351)
Increase (decrease) in tax resulting from: Proration									1,835	2,274	3,138
Increase (decrease) in tax resulting from: Tax audit settlement											(2,508)
Increase (decrease) in tax resulting from: Uncertain tax position release											(31,912)
Increase (decrease) in taxes resulting from: Other									(588)	27,238	5,381
Total income tax expense (benefit)									165,077	271,487	96,441
Non-U.S. [Member]
Income Taxes [Line Items]
Underwriting gain (loss)									658,421	491,909	216,228
Net investment income									270,069	273,589	312,820
Net realized capital gains (losses)									6,040	4,413	21,073
Net derivative gain (loss)									(11,599)	44,044	(9,738)
Corporate expenses									(16,169)	(16,555)	(15,211)
Interest, fee and bond issue cost amortization expense									(563)	(665)	(2,936)
Other income (expense)									19,998	1,598	(15,042)
INCOME (LOSS) BEFORE TAXES									926,197	798,333	507,194
Expected tax provision at the applicable statutory rate(s)									21,279	16,279	11,012
Increase (decrease) in taxes resulting from: Other									1,296	1,940	3,119
Total income tax expense (benefit)									$ 22,575	$ 18,219	$ 14,131