Unpaid losses and loss expenses Unpaid Losses and loss expenses, claims development (Cumulative Net incurred Loss and Allocated Loss Adjustment Expense) (Details) number in Thousands, $ in Millions	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	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 ($)	Dec. 31, 2008 USD ($)
Claims Development [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	$ 46,700
North America Commercial P&C Insurance - Workers' Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	11,327
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	4,937
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	2,483
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	8,873
North America Commercial P&C Insurance - Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	34,121
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	18,919
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	1,429
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	16,631
North America Commercial P&C Insurance - Other Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	5,185
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	3,633
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	237
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	1,789
North America Commercial P&C Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	17,229
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	14,854
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	23
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	2,398
North America Personal P&C Insurance [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	21,564
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	19,168
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	25
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	2,421
Overseas General Insurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	12,673
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	6,997
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	350
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	6,026
Overseas General Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	18,445
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	15,961
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	65
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	2,549
Global Reinsurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	3,320
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	2,339
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	359
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	1,340
Global Reinsurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	2,172
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	1,816
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	15
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	371
Short-duration Insurance Contracts, Accident Year 2008 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	993	$ 986	$ 1,004	$ 1,009	$ 1,010	$ 1,036	$ 1,037	$ 1,043	$ 1,042	$ 1,084
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	214
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 651	632	607	578	546	503	439	371	275	124
Short-duration Insurance Contracts, Number of Reported Claims	333
Short-duration Insurance Contracts, Accident Year 2008 [Member] | North America Commercial P&C Insurance - Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 3,157	3,174	3,278	3,352	3,412	3,652	3,791	3,812	3,823	3,792
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	245
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 2,836	2,753	2,657	2,558	2,323	1,992	1,643	1,110	580	147
Short-duration Insurance Contracts, Number of Reported Claims	21
Short-duration Insurance Contracts, Accident Year 2008 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 637	641	646	643	647	644	661	700	733	693
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	13
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 617	618	610	602	591	566	520	446	342	144
Short-duration Insurance Contracts, Number of Reported Claims	20
Short-duration Insurance Contracts, Accident Year 2008 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,859	1,863	1,865	1,877	1,881	1,890	1,901	1,916	1,941	1,999
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	5
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,851	1,848	1,847	1,838	1,832	1,823	1,794	1,744	1,622	965
Short-duration Insurance Contracts, Number of Reported Claims	999
Short-duration Insurance Contracts, Accident Year 2008 [Member] | North America Personal P&C Insurance [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,659	1,661	1,661	1,670	1,677	1,695	1,724	1,749	1,779	1,779
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	5
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,651	1,651	1,647	1,644	1,638	1,622	1,586	1,521	1,409	975
Short-duration Insurance Contracts, Number of Reported Claims	139
Short-duration Insurance Contracts, Accident Year 2008 [Member] | Overseas General Insurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,281	1,330	1,315	1,336	1,408	1,453	1,444	1,423	1,334	1,220
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	81
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,116	1,083	1,029	971	895	790	642	472	306	121
Short-duration Insurance Contracts, Number of Reported Claims	39
Short-duration Insurance Contracts, Accident Year 2008 [Member] | Overseas General Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,504	1,508	1,519	1,524	1,527	1,553	1,547	1,563	1,608	1,609
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	25
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,484	1,477	1,477	1,469	1,461	1,451	1,428	1,360	1,218	646
Short-duration Insurance Contracts, Number of Reported Claims	539
Short-duration Insurance Contracts, Accident Year 2008 [Member] | Global Reinsurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 399	401	404	408	407	428	431	439	420	399
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	48
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 315	305	295	277	253	220	176	131	77	33
Short-duration Insurance Contracts, Number of Reported Claims	1
Short-duration Insurance Contracts, Accident Year 2008 [Member] | Global Reinsurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 286	285	284	287	286	286	292	301	310	316
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	2
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 280	280	280	278	276	274	260	228	177	$ 79
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2009 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 965	972	966	977	980	990	997	998	1,029
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	233
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 617	597	550	519	475	416	348	258	107
Short-duration Insurance Contracts, Number of Reported Claims	282
Short-duration Insurance Contracts, Accident Year 2009 [Member] | North America Commercial P&C Insurance - Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 3,103	3,244	3,316	3,392	3,642	3,743	3,770	3,783	3,798
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	250
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 2,730	2,678	2,545	2,357	2,019	1,672	1,160	587	135
Short-duration Insurance Contracts, Number of Reported Claims	21
Short-duration Insurance Contracts, Accident Year 2009 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 441	445	447	454	488	531	550	584	594
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	2
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 428	423	414	402	374	337	287	206	70
Short-duration Insurance Contracts, Number of Reported Claims	15
Short-duration Insurance Contracts, Accident Year 2009 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,194	1,195	1,198	1,198	1,205	1,222	1,251	1,307	1,310
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	9
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,181	1,181	1,179	1,171	1,163	1,149	1,125	1,035	620
Short-duration Insurance Contracts, Number of Reported Claims	1,125
Short-duration Insurance Contracts, Accident Year 2009 [Member] | North America Personal P&C Insurance [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,533	1,534	1,538	1,538	1,545	1,554	1,568	1,598	1,611
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	7
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,523	1,521	1,513	1,503	1,486	1,439	1,347	1,236	887
Short-duration Insurance Contracts, Number of Reported Claims	125
Short-duration Insurance Contracts, Accident Year 2009 [Member] | Overseas General Insurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,202	1,256	1,257	1,365	1,482	1,485	1,474	1,425	1,284
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	76
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,020	993	896	824	763	667	524	341	123
Short-duration Insurance Contracts, Number of Reported Claims	39
Short-duration Insurance Contracts, Accident Year 2009 [Member] | Overseas General Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,366	1,366	1,377	1,377	1,395	1,415	1,446	1,534	1,564
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	3
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,343	1,344	1,341	1,335	1,324	1,300	1,233	1,095	602
Short-duration Insurance Contracts, Number of Reported Claims	518
Short-duration Insurance Contracts, Accident Year 2009 [Member] | Global Reinsurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 316	320	331	347	366	370	363	351	319
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	24
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 256	241	227	209	187	154	116	79	34
Short-duration Insurance Contracts, Number of Reported Claims	1
Short-duration Insurance Contracts, Accident Year 2009 [Member] | Global Reinsurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 139	139	139	141	144	150	152	172	141
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	3
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 134	134	134	134	132	129	122	106	$ 52
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2010 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,020	1,028	1,052	1,064	1,065	1,050	1,037	1,049
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	262
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 641	617	592	551	493	411	300	123
Short-duration Insurance Contracts, Number of Reported Claims	304
Short-duration Insurance Contracts, Accident Year 2010 [Member] | North America Commercial P&C Insurance - Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 3,107	3,128	3,250	3,419	3,559	3,601	3,583	3,578
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	423
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 2,527	2,426	2,259	1,893	1,559	1,108	611	126
Short-duration Insurance Contracts, Number of Reported Claims	20
Short-duration Insurance Contracts, Accident Year 2010 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 489	477	475	503	543	598	604	610
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	33
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 449	444	434	392	364	322	236	97
Short-duration Insurance Contracts, Number of Reported Claims	15
Short-duration Insurance Contracts, Accident Year 2010 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,410	1,416	1,420	1,428	1,430	1,466	1,543	1,507
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	9
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,397	1,396	1,393	1,384	1,359	1,323	1,223	724
Short-duration Insurance Contracts, Number of Reported Claims	1,059
Short-duration Insurance Contracts, Accident Year 2010 [Member] | North America Personal P&C Insurance [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,822	1,825	1,830	1,834	1,838	1,855	1,878	1,870
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	9
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,811	1,805	1,793	1,772	1,729	1,670	1,522	1,153
Short-duration Insurance Contracts, Number of Reported Claims	149
Short-duration Insurance Contracts, Accident Year 2010 [Member] | Overseas General Insurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,178	1,183	1,312	1,365	1,430	1,358	1,311	1,231
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	97
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 938	883	831	740	629	481	277	109
Short-duration Insurance Contracts, Number of Reported Claims	41
Short-duration Insurance Contracts, Accident Year 2010 [Member] | Overseas General Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,643	1,660	1,673	1,687	1,693	1,705	1,734	1,713
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	13
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,604	1,603	1,596	1,583	1,543	1,480	1,276	698
Short-duration Insurance Contracts, Number of Reported Claims	561
Short-duration Insurance Contracts, Accident Year 2010 [Member] | Global Reinsurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 402	416	426	432	443	432	421	401
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	55
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 307	292	274	249	221	179	125	56
Short-duration Insurance Contracts, Number of Reported Claims	1
Short-duration Insurance Contracts, Accident Year 2010 [Member] | Global Reinsurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 225	225	224	222	218	224	235	200
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	5
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 217	214	216	205	200	188	162	$ 56
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2011 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,012	1,022	1,053	1,049	1,046	1,030	1,037
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	294
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 595	567	533	484	411	294	119
Short-duration Insurance Contracts, Number of Reported Claims	287
Short-duration Insurance Contracts, Accident Year 2011 [Member] | North America Commercial P&C Insurance - Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 3,383	3,498	3,593	3,664	3,629	3,585	3,500
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	589
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 2,659	2,476	2,214	1,805	1,209	652	160
Short-duration Insurance Contracts, Number of Reported Claims	20
Short-duration Insurance Contracts, Accident Year 2011 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 513	521	530	545	578	586	577
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	33
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 466	461	437	400	341	235	86
Short-duration Insurance Contracts, Number of Reported Claims	16
Short-duration Insurance Contracts, Accident Year 2011 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,838	1,843	1,839	1,859	1,881	1,938	1,963
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	15
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,816	1,811	1,787	1,777	1,718	1,573	939
Short-duration Insurance Contracts, Number of Reported Claims	1,053
Short-duration Insurance Contracts, Accident Year 2011 [Member] | North America Personal P&C Insurance [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 2,159	2,160	2,164	2,173	2,185	2,210	2,208
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	13
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 2,138	2,129	2,105	2,051	1,971	1,835	1,360
Short-duration Insurance Contracts, Number of Reported Claims	168
Short-duration Insurance Contracts, Accident Year 2011 [Member] | Overseas General Insurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,094	1,109	1,176	1,262	1,270	1,277	1,272
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	157
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 795	719	638	534	400	250	91
Short-duration Insurance Contracts, Number of Reported Claims	42
Short-duration Insurance Contracts, Accident Year 2011 [Member] | Overseas General Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,901	1,908	1,920	1,939	1,978	2,035	1,950
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	7
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,841	1,832	1,817	1,786	1,728	1,520	793
Short-duration Insurance Contracts, Number of Reported Claims	579
Short-duration Insurance Contracts, Accident Year 2011 [Member] | Global Reinsurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 415	419	429	434	431	416	409
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	45
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 311	291	267	236	195	146	70
Short-duration Insurance Contracts, Number of Reported Claims	1
Short-duration Insurance Contracts, Accident Year 2011 [Member] | Global Reinsurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 264	264	263	262	272	275	274
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	1
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 258	255	251	232	207	176	$ 85
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2012 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 989	1,011	1,040	1,030	1,011	1,050
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	326
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 532	486	436	365	271	111
Short-duration Insurance Contracts, Number of Reported Claims	288
Short-duration Insurance Contracts, Accident Year 2012 [Member] | North America Commercial P&C Insurance - Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 3,426	3,524	3,564	3,613	3,628	3,552
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	856
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 2,326	2,092	1,680	1,172	656	166
Short-duration Insurance Contracts, Number of Reported Claims	20
Short-duration Insurance Contracts, Accident Year 2012 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 517	518	559	575	604	632
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	27
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 470	435	386	319	223	69
Short-duration Insurance Contracts, Number of Reported Claims	16
Short-duration Insurance Contracts, Accident Year 2012 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,848	1,861	1,866	1,884	1,918	2,034
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	11
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,822	1,795	1,766	1,698	1,577	715
Short-duration Insurance Contracts, Number of Reported Claims	1,037
Short-duration Insurance Contracts, Accident Year 2012 [Member] | North America Personal P&C Insurance [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 2,186	2,185	2,191	2,183	2,183	2,185
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	9
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 2,149	2,117	2,063	1,957	1,806	1,176
Short-duration Insurance Contracts, Number of Reported Claims	173
Short-duration Insurance Contracts, Accident Year 2012 [Member] | Overseas General Insurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,345	1,363	1,367	1,348	1,281	1,311
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	279
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 856	714	598	443	254	77
Short-duration Insurance Contracts, Number of Reported Claims	42
Short-duration Insurance Contracts, Accident Year 2012 [Member] | Overseas General Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,650	1,661	1,667	1,723	1,764	1,775
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	34
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,572	1,562	1,539	1,479	1,284	716
Short-duration Insurance Contracts, Number of Reported Claims	600
Short-duration Insurance Contracts, Accident Year 2012 [Member] | Global Reinsurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 372	379	394	391	383	387
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	23
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 308	292	261	222	167	77
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2012 [Member] | Global Reinsurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 187	189	191	200	210	232
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	2
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 177	172	166	156	129	$ 44
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2013 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,085	1,127	1,122	1,108	1,109
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	368
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 553	506	422	286	107
Short-duration Insurance Contracts, Number of Reported Claims	300
Short-duration Insurance Contracts, Accident Year 2013 [Member] | North America Commercial P&C Insurance - Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 3,430	3,532	3,542	3,541	3,546
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	1,090
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 2,007	1,597	1,192	548	130
Short-duration Insurance Contracts, Number of Reported Claims	20
Short-duration Insurance Contracts, Accident Year 2013 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 468	515	522	530	526
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	60
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 385	348	271	197	69
Short-duration Insurance Contracts, Number of Reported Claims	18
Short-duration Insurance Contracts, Accident Year 2013 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,340	1,360	1,337	1,424	1,434
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	18
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,311	1,285	1,237	1,138	651
Short-duration Insurance Contracts, Number of Reported Claims	1,074
Short-duration Insurance Contracts, Accident Year 2013 [Member] | North America Personal P&C Insurance [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,924	1,899	1,896	1,888	1,860
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	41
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,843	1,786	1,687	1,504	1,043
Short-duration Insurance Contracts, Number of Reported Claims	126
Short-duration Insurance Contracts, Accident Year 2013 [Member] | Overseas General Insurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,270	1,330	1,284	1,284	1,289
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	314
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 727	584	432	272	90
Short-duration Insurance Contracts, Number of Reported Claims	42
Short-duration Insurance Contracts, Accident Year 2013 [Member] | Overseas General Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,730	1,739	1,787	1,859	1,868
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	62
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,612	1,574	1,541	1,340	738
Short-duration Insurance Contracts, Number of Reported Claims	622
Short-duration Insurance Contracts, Accident Year 2013 [Member] | Global Reinsurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 331	330	330	327	321
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	41
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 242	222	186	143	65
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2013 [Member] | Global Reinsurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 144	143	149	160	163
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	5
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 133	131	121	103	$ 46
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2014 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,214	1,217	1,201	1,207
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	553
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 484	410	295	113
Short-duration Insurance Contracts, Number of Reported Claims	337
Short-duration Insurance Contracts, Accident Year 2014 [Member] | North America Commercial P&C Insurance - Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 3,717	3,674	3,585	3,535
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	1,526
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,804	1,250	679	164
Short-duration Insurance Contracts, Number of Reported Claims	21
Short-duration Insurance Contracts, Accident Year 2014 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 594	579	581	592
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	147
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 391	317	220	80
Short-duration Insurance Contracts, Number of Reported Claims	17
Short-duration Insurance Contracts, Accident Year 2014 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,561	1,581	1,663	1,647
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	29
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,505	1,484	1,373	820
Short-duration Insurance Contracts, Number of Reported Claims	1,102
Short-duration Insurance Contracts, Accident Year 2014 [Member] | North America Personal P&C Insurance [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 2,145	2,192	2,206	2,205
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	29
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 2,034	1,925	1,764	1,310
Short-duration Insurance Contracts, Number of Reported Claims	135
Short-duration Insurance Contracts, Accident Year 2014 [Member] | Overseas General Insurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,388	1,377	1,366	1,295
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	506
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 614	481	299	117
Short-duration Insurance Contracts, Number of Reported Claims	43
Short-duration Insurance Contracts, Accident Year 2014 [Member] | Overseas General Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,959	1,985	2,048	1,975
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	72
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,782	1,715	1,497	800
Short-duration Insurance Contracts, Number of Reported Claims	594
Short-duration Insurance Contracts, Accident Year 2014 [Member] | Global Reinsurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 343	340	334	333
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	46
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 249	218	185	92
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2014 [Member] | Global Reinsurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 182	179	179	163
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	9
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 162	151	128	$ 65
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,271	1,259	1,282
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	631
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 418	301	116
Short-duration Insurance Contracts, Number of Reported Claims	339
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Commercial P&C Insurance - Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 3,818	3,708	3,559
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	1,941
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,206	605	138
Short-duration Insurance Contracts, Number of Reported Claims	23
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 501	469	486
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	191
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 215	137	47
Short-duration Insurance Contracts, Number of Reported Claims	15
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,650	1,746	1,737
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	83
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,488	1,343	726
Short-duration Insurance Contracts, Number of Reported Claims	1,173
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Personal P&C Insurance [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 2,560	2,549	2,494
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	126
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 2,270	2,083	1,499
Short-duration Insurance Contracts, Number of Reported Claims	139
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Overseas General Insurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,353	1,324	1,223
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	542
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 504	296	92
Short-duration Insurance Contracts, Number of Reported Claims	45
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Overseas General Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 2,195	2,243	2,111
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	157
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,873	1,638	901
Short-duration Insurance Contracts, Number of Reported Claims	627
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Global Reinsurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 300	289	285
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	47
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 191	159	90
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Global Reinsurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 161	154	146
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	8
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 132	103	$ 56
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,367	1,367
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	806
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 326	122
Short-duration Insurance Contracts, Number of Reported Claims	310
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Commercial P&C Insurance - Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 3,594	3,533
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	2,381
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 663	171
Short-duration Insurance Contracts, Number of Reported Claims	24
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 494	503
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	249
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 146	52
Short-duration Insurance Contracts, Number of Reported Claims	15
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,888	1,911
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	168
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,504	846
Short-duration Insurance Contracts, Number of Reported Claims	1,293
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Personal P&C Insurance [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 2,542	2,439
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	248
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 2,051	1,453
Short-duration Insurance Contracts, Number of Reported Claims	140
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Overseas General Insurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,333	1,227
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	749
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 328	127
Short-duration Insurance Contracts, Number of Reported Claims	45
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Overseas General Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 2,148	2,164
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	19
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,752	1,083
Short-duration Insurance Contracts, Number of Reported Claims	637
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Global Reinsurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 228	224
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	63
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 113	57
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Global Reinsurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 188	182
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	17
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 132	$ 57
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,411
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	1,080
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 120
Short-duration Insurance Contracts, Number of Reported Claims	307
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Commercial P&C Insurance - Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 3,386
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	2,994
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 161
Short-duration Insurance Contracts, Number of Reported Claims	19
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 531
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	387
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 66
Short-duration Insurance Contracts, Number of Reported Claims	13
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 2,641
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	1,089
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 979
Short-duration Insurance Contracts, Number of Reported Claims	1,175
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Personal P&C Insurance [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 3,034
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	725
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,698
Short-duration Insurance Contracts, Number of Reported Claims	123
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Overseas General Insurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 1,229
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	968
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 99
Short-duration Insurance Contracts, Number of Reported Claims	34
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Overseas General Insurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 2,349
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	307
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,098
Short-duration Insurance Contracts, Number of Reported Claims	616
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Global Reinsurance - Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 214
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	121
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 47
Short-duration Insurance Contracts, Number of Reported Claims	0
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Global Reinsurance - Non-Casualty [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 396
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	82
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 191
Short-duration Insurance Contracts, Number of Reported Claims	0