Reserve For Losses, LAE And Future Policy Benefit Reserve (Ultimate Loss and ALAE And Paid Loss And ALAE, Net Of Reinsurance) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Claims Development [Line Items]
Liabilities for claims and claim adjustment expenses, net of reinsurance	$ 19,671
Reinsurance [Member] | Casualty Business [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	14,554
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,754
All outstanding liabilities prior to 2012, net of reinsurance	916
Liabilities for claims and claim adjustment expenses, net of reinsurance	9,715
Reinsurance [Member] | Casualty Business [Member] | 2013 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	684	$ 694	$ 699	$ 699	$ 719	$ 748	$ 779	$ 788	$ 801	$ 710
Total of IBNR Liabilities Plus Expected Development on Reported Claims	11
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	603	593	565	540	489	383	310	211	121	48
Reinsurance [Member] | Casualty Business [Member] | 2014 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	720	730	732	719	741	783	807	800	762
Total of IBNR Liabilities Plus Expected Development on Reported Claims	13
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	607	585	545	501	426	301	212	122	57
Reinsurance [Member] | Casualty Business [Member] | 2015 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	829	832	832	795	811	814	818	777
Total of IBNR Liabilities Plus Expected Development on Reported Claims	47
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	647	611	565	497	408	263	157	57
Reinsurance [Member] | Casualty Business [Member] | 2016 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	965	935	933	857	862	865	790
Total of IBNR Liabilities Plus Expected Development on Reported Claims	91
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	690	614	539	426	320	187	88
Reinsurance [Member] | Casualty Business [Member] | 2017 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	982	926	918	837	830	870
Total of IBNR Liabilities Plus Expected Development on Reported Claims	132
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	677	575	455	316	185	80
Reinsurance [Member] | Casualty Business [Member] | 2018 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	1,485	1,416	1,386	1,309	1,311
Total of IBNR Liabilities Plus Expected Development on Reported Claims	354
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	803	616	456	284	154
Reinsurance [Member] | Casualty Business [Member] | 2019 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	1,775	1,751	1,748	1,683
Total of IBNR Liabilities Plus Expected Development on Reported Claims	727
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	718	511	338	208
Reinsurance [Member] | Casualty Business [Member] | 2020 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	1,846	1,867	1,896
Total of IBNR Liabilities Plus Expected Development on Reported Claims	1,178
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	489	300	190
Reinsurance [Member] | Casualty Business [Member] | 2021 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	2,449	2,454
Total of IBNR Liabilities Plus Expected Development on Reported Claims	1,829
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	318	214
Reinsurance [Member] | Casualty Business [Member] | 2022 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	2,818
Total of IBNR Liabilities Plus Expected Development on Reported Claims	2,133
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	200
Reinsurance [Member] | Property Business [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	20,594
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	15,134
All outstanding liabilities prior to 2012, net of reinsurance	103
Liabilities for claims and claim adjustment expenses, net of reinsurance	5,562
Reinsurance [Member] | Property Business [Member] | 2013 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	757	758	758	760	753	757	763	819	930	1,275
Total of IBNR Liabilities Plus Expected Development on Reported Claims	2
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	735	733	733	732	723	713	693	638	510	375
Reinsurance [Member] | Property Business [Member] | 2014 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	928	930	930	937	933	937	1,030	1,181	1,343
Total of IBNR Liabilities Plus Expected Development on Reported Claims	3
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	893	892	891	884	874	842	769	641	366
Reinsurance [Member] | Property Business [Member] | 2015 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	943	946	945	952	950	976	1,053	1,386
Total of IBNR Liabilities Plus Expected Development on Reported Claims	2
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	905	900	891	869	842	759	607	377
Reinsurance [Member] | Property Business [Member] | 2016 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	1,523	1,527	1,526	1,548	1,554	1,518	1,695
Total of IBNR Liabilities Plus Expected Development on Reported Claims	10
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,454	1,441	1,421	1,367	1,249	961	469
Reinsurance [Member] | Property Business [Member] | 2017 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	3,703	3,692	3,647	3,518	3,407	2,784
Total of IBNR Liabilities Plus Expected Development on Reported Claims	3
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,426	3,332	3,130	2,744	2,180	819
Reinsurance [Member] | Property Business [Member] | 2018 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	2,379	2,426	2,488	2,486	2,611
Total of IBNR Liabilities Plus Expected Development on Reported Claims	24
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,136	2,065	1,878	1,525	545
Reinsurance [Member] | Property Business [Member] | 2019 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	1,899	2,015	2,070	2,038
Total of IBNR Liabilities Plus Expected Development on Reported Claims	29
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,667	1,505	1,185	730
Reinsurance [Member] | Property Business [Member] | 2020 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	2,425	2,481	2,408
Total of IBNR Liabilities Plus Expected Development on Reported Claims	240
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,733	1,321	584
Reinsurance [Member] | Property Business [Member] | 2021 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	2,780	2,754
Total of IBNR Liabilities Plus Expected Development on Reported Claims	476
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,534	684
Reinsurance [Member] | Property Business [Member] | 2022 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	3,257
Total of IBNR Liabilities Plus Expected Development on Reported Claims	1,898
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	652
Insurance [Member] | Casualty Business [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	7,703
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,003
All outstanding liabilities prior to 2012, net of reinsurance	127
Liabilities for claims and claim adjustment expenses, net of reinsurance	3,828
Insurance [Member] | Casualty Business [Member] | 2013 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	347	350	350	351	344	351	393	393	393	393
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 25
Cumulative Number of Reported Claims	22,031
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 321	317	311	304	286	260	225	176	117	33
Insurance [Member] | Casualty Business [Member] | 2014 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	398	397	398	397	396	460	454	457	431
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 32
Cumulative Number of Reported Claims	26,449
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 360	350	339	325	297	257	202	125	41
Insurance [Member] | Casualty Business [Member] | 2015 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	477	471	471	467	541	535	527	519
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 40
Cumulative Number of Reported Claims	29,020
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 435	413	382	353	292	219	135	44
Insurance [Member] | Casualty Business [Member] | 2016 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	540	538	549	612	579	550	552
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 53
Cumulative Number of Reported Claims	34,164
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 481	443	400	341	268	164	55
Insurance [Member] | Casualty Business [Member] | 2017 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	629	628	652	620	600	610
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 85
Cumulative Number of Reported Claims	38,344
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 529	453	378	280	172	54
Insurance [Member] | Casualty Business [Member] | 2018 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	769	755	742	705	701
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 154
Cumulative Number of Reported Claims	39,029
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 594	443	317	207	63
Insurance [Member] | Casualty Business [Member] | 2019 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	885	876	844	848
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 204
Cumulative Number of Reported Claims	42,006
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 551	397	234	72
Insurance [Member] | Casualty Business [Member] | 2020 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	1,043	1,049	993
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 416
Cumulative Number of Reported Claims	39,545
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 388	236	66
Insurance [Member] | Casualty Business [Member] | 2021 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	1,246	1,189
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 732
Cumulative Number of Reported Claims	44,274
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 261	109
Insurance [Member] | Casualty Business [Member] | 2022 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	1,367
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 865
Cumulative Number of Reported Claims	37,739
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 85
Insurance [Member] | Property Business [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	3,789
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,223
All outstanding liabilities prior to 2012, net of reinsurance
Liabilities for claims and claim adjustment expenses, net of reinsurance	566
Insurance [Member] | Property Business [Member] | 2013 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	92	92	92	92	92	92	92	91	98	112
Total of IBNR Liabilities Plus Expected Development on Reported Claims
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	92	92	92	92	92	92	92	92	93	$ 69
Insurance [Member] | Property Business [Member] | 2014 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	120	119	119	119	119	119	120	123	132
Total of IBNR Liabilities Plus Expected Development on Reported Claims	1
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	119	119	119	119	118	118	118	116	$ 82
Insurance [Member] | Property Business [Member] | 2015 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	150	146	146	144	146	144	153	173
Total of IBNR Liabilities Plus Expected Development on Reported Claims	1
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	147	147	146	146	145	142	141	$ 102
Insurance [Member] | Property Business [Member] | 2016 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	294	294	292	289	279	274	288
Total of IBNR Liabilities Plus Expected Development on Reported Claims
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	293	293	290	287	271	249	$ 162
Insurance [Member] | Property Business [Member] | 2017 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	504	489	495	492	499	494
Total of IBNR Liabilities Plus Expected Development on Reported Claims
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	499	496	479	457	423	$ 179
Insurance [Member] | Property Business [Member] | 2018 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	422	407	394	400	405
Total of IBNR Liabilities Plus Expected Development on Reported Claims	1
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	418	404	376	357	$ 245
Insurance [Member] | Property Business [Member] | 2019 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	363	351	347	347
Total of IBNR Liabilities Plus Expected Development on Reported Claims	1
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	357	339	315	$ 227
Insurance [Member] | Property Business [Member] | 2020 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	498	507	599
Total of IBNR Liabilities Plus Expected Development on Reported Claims	27
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	453	416	$ 293
Insurance [Member] | Property Business [Member] | 2021 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	579	646
Total of IBNR Liabilities Plus Expected Development on Reported Claims	66
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	473	$ 328
Insurance [Member] | Property Business [Member] | 2022 [Member]
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of reinsurance	767
Total of IBNR Liabilities Plus Expected Development on Reported Claims	273
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 372