Losses and Loss Expenses - Information about incurred and paid claims development - Insurance - EPC (Details) $ in Thousands		Dec. 31, 2016 USD ($) Claim	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)	Dec. 31, 2007 USD ($)
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		$ 53,162,870
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		35,612,206
All outstanding liabilities prior to 2007, net of reinsurance		2,501,779
Liabilities for unpaid losses and loss expenses, net of reinsurance		20,052,443
Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		38,032,090
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		25,758,860
All outstanding liabilities prior to 2007, net of reinsurance		1,069,908
Liabilities for unpaid losses and loss expenses, net of reinsurance		13,343,138
EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,691,915
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		5,480,891
All outstanding liabilities prior to 2007, net of reinsurance		24,692
Liabilities for unpaid losses and loss expenses, net of reinsurance		1,235,716
Accident Year 2007
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,390,981	$ 4,432,150	$ 4,519,599	$ 4,541,978	$ 4,569,019	$ 4,689,256	$ 4,684,540	$ 4,718,961	$ 4,806,850	$ 4,632,657
IBNR (1)	[1]	246,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,894,280	3,822,207	3,744,872	3,612,934	3,397,370	3,126,834	2,587,918	2,055,288	1,289,961	521,083
Accident Year 2007 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,246,355	3,274,775	3,318,423	3,317,676	3,329,848	3,442,331	3,431,600	3,426,696	3,490,955	3,258,668
IBNR (1)	[1]	$ 158,351
Number of Claims | Claim		45,542
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,943,144	2,896,977	2,822,610	2,715,861	2,549,256	2,333,047	1,884,318	1,462,857	930,428	367,171
Accident Year 2007 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		355,709	356,106	357,009	358,820	361,632	364,454	365,395	385,373	394,730	439,938
IBNR (1)		$ (213)
Number of Claims | Claim		5,380
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 351,151	350,602	348,059	347,421	341,442	329,883	316,321	298,622	208,210	$ 69,288
Accident Year 2008
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,322,204	5,357,648	5,417,072	5,449,364	5,479,907	5,524,325	5,503,422	5,575,015	5,504,796
IBNR (1)	[1]	307,738
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,700,567	4,582,409	4,450,875	4,240,640	3,947,203	3,446,415	2,857,474	1,994,235	788,760
Accident Year 2008 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,786,671	3,822,133	3,857,758	3,889,538	3,918,450	3,974,071	3,935,499	3,969,259	3,891,682
IBNR (1)	[1]	$ 186,723
Number of Claims | Claim		54,952
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,415,212	3,337,607	3,234,869	3,069,812	2,843,188	2,427,033	1,973,577	1,339,577	461,606
Accident Year 2008 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		767,031	768,610	774,108	769,906	777,476	782,005	806,976	834,562	841,913
IBNR (1)		$ 10,701
Number of Claims | Claim		9,013
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 750,022	747,374	752,294	748,607	730,513	653,749	604,163	467,537	$ 152,946
Accident Year 2009
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,392,904	4,422,167	4,550,542	4,550,362	4,556,902	4,542,408	4,627,569	4,622,547
IBNR (1)	[1]	317,583
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,663,224	3,551,474	3,366,917	3,117,922	2,655,163	2,192,791	1,530,295	638,179
Accident Year 2009 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,346,817	3,369,614	3,500,575	3,483,027	3,480,715	3,458,320	3,499,124	3,472,222
IBNR (1)	[1]	$ 190,193
Number of Claims | Claim		54,896
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,865,558	2,787,167	2,634,783	2,432,021	2,043,196	1,666,673	1,140,796	462,090
Accident Year 2009 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		342,072	344,108	345,668	349,819	356,069	364,526	382,644	400,045
IBNR (1)		$ 6,549
Number of Claims | Claim		7,596
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 331,246	328,222	313,434	311,335	287,809	254,420	190,194	$ 84,638
Accident Year 2010
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,981,939	4,957,474	4,974,782	5,026,101	5,002,061	5,111,634	4,983,044
IBNR (1)	[1]	464,306
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,084,244	3,851,827	3,521,163	3,144,278	2,645,868	1,855,407	840,030
Accident Year 2010 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,697,761	3,661,919	3,688,045	3,735,809	3,699,234	3,809,102	3,702,458
IBNR (1)	[1]	$ 313,815
Number of Claims | Claim		61,416
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,072,546	2,914,856	2,685,015	2,370,062	1,978,027	1,377,513	607,658
Accident Year 2010 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		568,574	574,091	565,494	571,375	589,119	611,917	596,340
IBNR (1)		$ (5,681)
Number of Claims | Claim		8,532
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 547,486	542,011	543,985	526,375	476,832	380,649	$ 166,353
Accident Year 2011
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,083,796	6,116,046	5,980,635	6,111,779	6,187,474	6,236,775
IBNR (1)	[1]	558,008
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		5,021,000	4,737,827	4,242,053	3,664,970	2,872,319	1,246,596
Accident Year 2011 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,001,271	4,026,511	3,921,559	4,009,166	3,986,420	4,014,389
IBNR (1)	[1]	$ 379,349
Number of Claims | Claim		65,437
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,290,213	3,062,399	2,653,619	2,216,640	1,617,155	649,690
Accident Year 2011 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		842,481	846,315	857,510	890,820	911,684	979,353
IBNR (1)		$ 7,165
Number of Claims | Claim		10,172
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 815,694	813,298	784,418	744,330	610,086	$ 211,176
Accident Year 2012
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,663,926	5,754,387	5,640,576	5,660,616	5,697,958
IBNR (1)	[1]	715,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,199,766	3,802,042	3,149,842	2,256,973	952,158
Accident Year 2012 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,851,259	3,921,415	3,800,046	3,799,876	3,870,871
IBNR (1)	[1]	$ 468,002
Number of Claims | Claim		70,919
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,886,674	2,578,639	2,079,400	1,471,761	634,043
Accident Year 2012 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		626,132	636,896	635,712	660,128	689,032
IBNR (1)		$ 6,086
Number of Claims | Claim		11,131
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 593,981	574,467	531,299	389,827	$ 161,117
Accident Year 2013
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,426,144	5,523,695	5,554,791	5,558,316
IBNR (1)	[1]	1,082,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,614,076	3,049,907	2,194,912	976,023
Accident Year 2013 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,924,048	3,978,956	4,003,359	3,942,360
IBNR (1)	[1]	$ 802,611
Number of Claims | Claim		78,018
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,597,422	2,141,332	1,509,232	657,753
Accident Year 2013 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		684,578	690,102	715,909	740,573
IBNR (1)		$ 9,763
Number of Claims | Claim		12,141
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 636,623	586,539	452,805	$ 165,460
Accident Year 2014
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,397,264	5,369,393	5,183,056
IBNR (1)	[1]	1,396,883
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,090,343	2,250,446	957,525
Accident Year 2014 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,978,436	3,917,364	3,748,154
IBNR (1)	[1]	$ 1,052,314
Number of Claims | Claim		87,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,263,643	1,597,123	669,745
Accident Year 2014 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		723,382	735,789	703,860
IBNR (1)	[1]	$ 6,921
Number of Claims | Claim		14,609
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 645,682	504,925	$ 180,735
Accident Year 2015
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,498,206	5,354,494
IBNR (1)	[1]	1,962,006
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		2,152,569	970,277
Accident Year 2015 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,039,203	3,849,731
IBNR (1)	[1]	$ 1,418,476
Number of Claims | Claim		94,229
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 1,563,019	691,253
Accident Year 2015 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		812,247	791,724
IBNR (1)		$ 64,949
Number of Claims | Claim		16,424
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 484,431	$ 224,497
Accident Year 2016
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,005,506
IBNR (1)	[1]	3,425,518
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,192,137
Accident Year 2016 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,160,269
IBNR (1)	[1]	$ 2,358,172
Number of Claims | Claim		65,684
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 861,429
Accident Year 2016 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		969,709
IBNR (1)		$ 228,630
Number of Claims | Claim		15,279
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 324,575

[1] Total IBNR Liabilities Plus Expected Development on Reported Claims