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INSURANCE LIABILITIES (Details - Undiscounted, Incurred and Paid Losses and Allocated Loss Adjustment Expenses)
$ in Millions
12 Months Ended
Dec. 31, 2021
USD ($)
item
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Dec. 31, 2012
USD ($)
Claims Development [Line Items]                    
Prior Year Development $ 78                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (171) $ (90) $ (340)              
Liabilities for losses and loss adjustment expenses, net of reinsurance 43,813 43,289 47,259 $ 51,949            
U.S. Workers Compensation                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 12,065                  
Prior Year Development (403)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (617) (367) (699)              
Incurred Impact of Adverse Development Reinsurance Agreement (5,256)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 10,253                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 7,286                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance 4,635                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 9,414                  
U.S. Workers Compensation | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 214                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 126                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (3,570)                  
Unallocated Loss Adjustment Expense Prior Year Development (98)                  
U.S. Excess Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 10,185                  
Prior Year Development 81                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 51 (149) 76              
Incurred Impact of Adverse Development Reinsurance Agreement (2,990)                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 5,541                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance 2,196                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 6,840                  
U.S. Excess Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 30                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 129                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (1,680)                  
Unallocated Loss Adjustment Expense Prior Year Development 79                  
U.S. Other Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 13,560                  
Prior Year Development 74                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (1) (141) 168              
Incurred Impact of Adverse Development Reinsurance Agreement (1,754)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 12,629                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 9,436                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance 1,435                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 5,559                  
U.S. Other Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 75                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 177                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (1,000)                  
Unallocated Loss Adjustment Expense Prior Year Development 47                  
U.S. Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 18,176                  
Prior Year Development 564                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 649 479 463              
Incurred Impact of Adverse Development Reinsurance Agreement (760)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 17,272                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 12,198                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance 138                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 6,116                  
U.S. Financial Lines | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (85)                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 326                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (182)                  
Unallocated Loss Adjustment Expense Prior Year Development 15                  
U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 34,934                  
Prior Year Development 204                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 172 (80) (204)              
Incurred Impact of Adverse Development Reinsurance Agreement (304)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 34,709                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 28,355                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance 340                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 6,919                  
U.S. Property and Special Risks | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 32                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 47                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (126)                  
Unallocated Loss Adjustment Expense Prior Year Development 7                  
U.S. Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 15,656                  
Prior Year Development (411)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (412) 94 (96)              
Incurred Impact of Adverse Development Reinsurance Agreement (11)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 15,644                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 14,582                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (62)                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 1,012                  
U.S. Personal Insurance | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 1                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 6                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (5)                  
UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 13,716                  
Prior Year Development 210                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 210 258 161              
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 7,339                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance 798                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 7,175                  
UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 13,781                  
Prior Year Development (118)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (118) (155) (108)              
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 11,204                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance 54                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 2,631                  
UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 25,866                  
Prior Year Development (173)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (173) (39) (119)              
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 23,950                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance 46                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 1,962                  
Other Operations Run-Off                    
Claims Development [Line Items]                    
Prior Year Development 86                  
All Other                    
Claims Development [Line Items]                    
Prior Year Development (36)                  
Prior to 2012                    
Claims Development [Line Items]                    
Reserve strengthening charges (569) (457) (266)              
Prior to 2012 | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Prior Year Development (31)                  
Reserve strengthening charges (365) (87) (210)              
Prior to 2012 | U.S. Workers Compensation | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 334                  
Prior to 2012 | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Prior Year Development (112)                  
Reserve strengthening charges (84) (237) 54              
Prior to 2012 | U.S. Excess Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (28)                  
Prior to 2012 | U.S. Other Casualty                    
Claims Development [Line Items]                    
Prior Year Development (46)                  
Reserve strengthening charges (17) (40) (170)              
Prior to 2012 | U.S. Other Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (29)                  
Prior to 2012 | U.S. Financial Lines                    
Claims Development [Line Items]                    
Prior Year Development (63)                  
Reserve strengthening charges (20) 25 11              
Prior to 2012 | U.S. Financial Lines | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (43)                  
Prior to 2012 | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Prior Year Development 4                  
Reserve strengthening charges (10) (6) (3)              
Prior to 2012 | U.S. Property and Special Risks | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 14                  
Prior to 2012 | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Prior Year Development 4                  
Reserve strengthening charges 3 3 1              
Prior to 2012 | U.S. Personal Insurance | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 1                  
Prior to 2012 | UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
Reserve strengthening charges (50) 6 9              
Prior to 2012 | UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
Reserve strengthening charges (13) 0 (28)              
Prior to 2012 | UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
Reserve strengthening charges (10) 3 0              
Prior to 2012 | Other Operations Run-Off                    
Claims Development [Line Items]                    
Reserve strengthening charges (10) 4 (46)              
Prior to 2012 | All Other                    
Claims Development [Line Items]                    
Reserve strengthening charges 7 (128) 116              
Total | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Prior Year Development (302)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (280)                  
Incurred Impact of Adverse Development Reinsurance Agreement (1,812)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 10,253 9,958 9,549 9,067 $ 8,032 $ 7,208        
Total | U.S. Workers Compensation | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (22)                  
Incurred Impact of Adverse Development Reinsurance Agreement (1,812) (1,790) (1,869) (1,940) (2,171) (2,216)        
Total | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Prior Year Development 101                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 122                  
Incurred Impact of Adverse Development Reinsurance Agreement (1,439)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 8,746 8,367 7,744 7,101 6,017 4,937        
Total | U.S. Excess Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (21)                  
Incurred Impact of Adverse Development Reinsurance Agreement (1,439) (1,418) (1,480) (1,493) (1,412) (1,544)        
Total | U.S. Other Casualty                    
Claims Development [Line Items]                    
Prior Year Development 92                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 35                  
Incurred Impact of Adverse Development Reinsurance Agreement (931)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 12,629 11,742 11,327 9,913 9,153 8,504        
Total | U.S. Other Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 57                  
Incurred Impact of Adverse Development Reinsurance Agreement (931) (988) (955) (992) (1,222) (1,060)        
Total | U.S. Financial Lines                    
Claims Development [Line Items]                    
Prior Year Development 567                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 624                  
Incurred Impact of Adverse Development Reinsurance Agreement (904)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 17,272 15,275 13,753 11,856 9,914 8,115        
Total | U.S. Financial Lines | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (57)                  
Incurred Impact of Adverse Development Reinsurance Agreement (904) (847) (733) (712) (720) (745)        
Total | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Prior Year Development 206                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 195                  
Incurred Impact of Adverse Development Reinsurance Agreement (225)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 34,709 30,949 26,518 23,945 20,777 15,410        
Total | U.S. Property and Special Risks | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 11                  
Incurred Impact of Adverse Development Reinsurance Agreement (225) (236) (234) (197) (222) (262)        
Total | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Prior Year Development (415)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (415)                  
Incurred Impact of Adverse Development Reinsurance Agreement (12)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 15,644 15,311 14,267 12,768 10,315 8,438        
Total | U.S. Personal Insurance | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement (12) (12) (12) (27) (36) (27)        
Total | UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 260                  
Total | UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (105)                  
Total | UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (163)                  
2012 | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,218 2,224 2,247 2,259 2,308 2,334 $ 2,260 $ 2,286 $ 2,194 $ 2,382
Prior Year Development 12                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (6)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 207                  
Cumulative Number of Reported Claims | item 72,021                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (380)                  
IBNR Impact of Adverse Development Reinsurance Agreement (192)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,838 1,826 1,804 1,793 1,814 1,819        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 15                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,763 1,719 1,669 1,632 1,563 1,440 1,272 1,089 804 415
Paid Impact of Adverse Development Reinsurance Agreement (33)                  
2012 | U.S. Workers Compensation | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 18                  
Incurred Impact of Adverse Development Reinsurance Agreement (380) (398) (443) (466) (494) (515)        
2012 | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,428 1,390 1,502 1,558 1,486 1,537 1,488 1,242 1,403 1,607
Prior Year Development (5)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 38                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 201                  
Cumulative Number of Reported Claims | item 3,844                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (296)                  
IBNR Impact of Adverse Development Reinsurance Agreement (154)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,132 1,137 1,214 1,254 1,163 1,175        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 47                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,111 1,090 1,121 1,022 887 649 495 288 106 3
Paid Impact of Adverse Development Reinsurance Agreement (24)                  
2012 | U.S. Excess Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (43)                  
Incurred Impact of Adverse Development Reinsurance Agreement (296) (253) (288) (304) (323) (362)        
2012 | U.S. Other Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,338 2,321 2,328 2,343 2,407 2,352 2,203 2,193 2,139 1,986
Prior Year Development (1)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 17                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 138                  
Cumulative Number of Reported Claims | item 44,226                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (204)                  
IBNR Impact of Adverse Development Reinsurance Agreement (110)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 2,134 2,135 2,159 2,175 2,197 2,189        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 28                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 2,130 2,101 2,053 2,009 1,869 1,677 1,385 1,042 739 411
Paid Impact of Adverse Development Reinsurance Agreement (23)                  
2012 | U.S. Other Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (18)                  
Incurred Impact of Adverse Development Reinsurance Agreement (204) (186) (169) (168) (210) (163)        
2012 | U.S. Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,067 2,082 2,077 2,015 1,990 1,988 1,907 1,800 1,763 1,592
Prior Year Development 2                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (15)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 63                  
Cumulative Number of Reported Claims 20,094                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (117)                  
IBNR Impact of Adverse Development Reinsurance Agreement (52)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,950 1,948 1,962 1,925 1,907 1,906        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 11                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,925 1,904 1,859 1,687 1,622 1,494 1,250 812 403 73
Paid Impact of Adverse Development Reinsurance Agreement (19)                  
2012 | U.S. Financial Lines | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 17                  
Incurred Impact of Adverse Development Reinsurance Agreement (117) (134) (115) (90) (83) (82)        
2012 | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 4,272 4,282 4,285 4,301 4,319 4,327 4,215 4,257 4,276 4,166
Prior Year Development (3)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (10)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 39                  
Cumulative Number of Reported Claims | item 48,478                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (16)                  
IBNR Impact of Adverse Development Reinsurance Agreement (6)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 4,256 4,259 4,259 4,282 4,294 4,300        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 33                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 4,204 4,195 4,180 4,146 4,114 3,985 3,768 3,404 2,709 840
Paid Impact of Adverse Development Reinsurance Agreement (5)                  
2012 | U.S. Property and Special Risks | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 7                  
Incurred Impact of Adverse Development Reinsurance Agreement (16) (23) (26) (19) (25) (27)        
2012 | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,100 2,101 2,099 2,095 2,094 2,077 2,083 2,109 2,128 2,208
Prior Year Development (1)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (1)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 0                  
Cumulative Number of Reported Claims | item 404,039                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (1)                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 2,099 2,100 2,098 2,093 2,091 2,088        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 0                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 2,099 2,098 2,095 2,085 2,079 2,065 2,035 1,996 1,936 1,238
Paid Impact of Adverse Development Reinsurance Agreement (1)                  
2012 | U.S. Personal Insurance | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement (1) (1) (1) (2) (3) 11        
2012 | UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,246 1,240 1,226 1,240 1,175 1,198 1,136 1,060 1,095 1,116
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 6                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 38                  
Cumulative Number of Reported Claims | item 141,043                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 1,079 1,056 1,026 965 861 769 636 456 311 108
2012 | UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,104 1,103 1,096 1,115 1,130 1,125 1,144 1,160 1,230 1,336
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 1                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 6                  
Cumulative Number of Reported Claims | item 40,170                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 1,085 1,081 1,080 1,073 1,064 1,038 991 922 730 281
2012 | UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,812 2,813 2,814 2,815 2,818 2,828 2,819 2,834 2,853 2,871
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (1)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 1                  
Cumulative Number of Reported Claims | item 1,730,022                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 2,802 2,798 2,793 2,785 2,768 2,739 2,682 2,576 2,348 $ 1,603
2013 | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,877 1,886 1,916 1,974 2,032 2,060 1,950 1,880 1,932  
Prior Year Development (16)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (9)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 190                  
Cumulative Number of Reported Claims | item 48,167                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (373)                  
IBNR Impact of Adverse Development Reinsurance Agreement (177)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,504 1,520 1,458 1,481 1,494 1,500        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 13                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,422 1,372 1,335 1,287 1,214 1,067 879 619 282  
Paid Impact of Adverse Development Reinsurance Agreement (38)                  
2013 | U.S. Workers Compensation | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (7)                  
Incurred Impact of Adverse Development Reinsurance Agreement (373) (366) (458) (493) (538) (560)        
2013 | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,303 1,316 1,292 1,282 1,241 1,308 1,169 1,035 1,123  
Prior Year Development 0                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (13)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 224                  
Cumulative Number of Reported Claims | item 3,315                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (333)                  
IBNR Impact of Adverse Development Reinsurance Agreement (182)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 970 970 1,032 981 932 935        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 42                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 903 882 819 705 578 387 207 105 15  
Paid Impact of Adverse Development Reinsurance Agreement (21)                  
2013 | U.S. Excess Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 13                  
Incurred Impact of Adverse Development Reinsurance Agreement (333) (346) (260) (301) (309) (373)        
2013 | U.S. Other Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,178 2,196 2,211 2,164 2,185 2,148 1,912 1,729 1,653  
Prior Year Development 6                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (18)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 194                  
Cumulative Number of Reported Claims | item 40,126                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (252)                  
IBNR Impact of Adverse Development Reinsurance Agreement (165)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,926 1,920 1,948 1,929 1,960 1,948        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 29                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,900 1,885 1,809 1,688 1,485 1,248 962 594 169  
Paid Impact of Adverse Development Reinsurance Agreement (16)                  
2013 | U.S. Other Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 24                  
Incurred Impact of Adverse Development Reinsurance Agreement (252) (276) (263) (235) (225) (200)        
2013 | U.S. Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,542 1,550 1,509 1,497 1,555 1,613 1,670 1,719 1,790  
Prior Year Development 13                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (8)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 35                  
Cumulative Number of Reported Claims 19,150                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (127)                  
IBNR Impact of Adverse Development Reinsurance Agreement (32)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,415 1,402 1,409 1,408 1,429 1,442        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 3                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,440 1,362 1,314 1,235 1,139 945 682 327 41  
Paid Impact of Adverse Development Reinsurance Agreement (63)                  
2013 | U.S. Financial Lines | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 21                  
Incurred Impact of Adverse Development Reinsurance Agreement (127) (148) (100) (89) (126) (171)        
2013 | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,422 2,433 2,440 2,449 2,447 2,434 2,389 2,531 2,528  
Prior Year Development (7)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (11)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 27                  
Cumulative Number of Reported Claims | item 49,990                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (32)                  
IBNR Impact of Adverse Development Reinsurance Agreement (16)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 2,390 2,397 2,402 2,422 2,409 2,407        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 11                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 2,355 2,345 2,326 2,301 2,189 2,042 1,849 1,571 734  
Paid Impact of Adverse Development Reinsurance Agreement (5)                  
2013 | U.S. Property and Special Risks | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 4                  
Incurred Impact of Adverse Development Reinsurance Agreement (32) (36) (38) (27) (38) (27)        
2013 | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,777 1,778 1,777 1,776 1,780 1,782 1,803 1,816 1,887  
Prior Year Development 0                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (1)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 1                  
Cumulative Number of Reported Claims | item 335,374                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (1)                  
IBNR Impact of Adverse Development Reinsurance Agreement (1)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,776 1,776 1,776 1,774 1,774 1,774        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 0                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,775 1,774 1,772 1,766 1,759 1,744 1,705 1,634 1,109  
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2013 | U.S. Personal Insurance | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 1                  
Incurred Impact of Adverse Development Reinsurance Agreement (1) (2) (1) (2) (6) (8)        
2013 | UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,212 1,218 1,194 1,149 1,075 1,069 1,087 1,114 1,068  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (6)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 63                  
Cumulative Number of Reported Claims | item 109,088                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 1,040 1,007 957 875 756 637 499 347 92  
2013 | UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,246 1,247 1,256 1,274 1,283 1,298 1,319 1,430 1,438  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (1)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 2                  
Cumulative Number of Reported Claims | item 40,053                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 1,219 1,217 1,211 1,200 1,179 1,129 1,053 825 336  
2013 | UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,671 2,673 2,674 2,677 2,681 2,686 2,686 2,721 2,720  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (2)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 3                  
Cumulative Number of Reported Claims | item 1,736,664                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 2,663 2,657 2,650 2,638 2,607 2,551 2,445 2,229 $ 1,492  
2014 | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,637 1,679 1,709 1,794 1,862 1,866 1,764 1,729    
Prior Year Development (52)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (42)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 292                  
Cumulative Number of Reported Claims | item 40,776                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (466)                  
IBNR Impact of Adverse Development Reinsurance Agreement (269)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,171 1,223 1,329 1,309 1,310 1,311        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 23                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,180 1,137 1,096 1,030 930 786 558 231    
Paid Impact of Adverse Development Reinsurance Agreement (31)                  
2014 | U.S. Workers Compensation | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (10)                  
Incurred Impact of Adverse Development Reinsurance Agreement (466) (456) (380) (485) (552) (555)        
2014 | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,269 1,248 1,283 1,339 1,260 1,275 1,069 938    
Prior Year Development 37                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 21                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 288                  
Cumulative Number of Reported Claims | item 2,839                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (320)                  
IBNR Impact of Adverse Development Reinsurance Agreement (155)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 949 912 844 915 905 902        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 133                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 839 815 703 590 444 240 77 3    
Paid Impact of Adverse Development Reinsurance Agreement (28)                  
2014 | U.S. Excess Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 16                  
Incurred Impact of Adverse Development Reinsurance Agreement (320) (336) (439) (424) (355) (373)        
2014 | U.S. Other Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,935 1,946 1,916 1,910 2,009 1,963 1,721 1,751    
Prior Year Development 21                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (11)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 120                  
Cumulative Number of Reported Claims | item 38,149                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (213)                  
IBNR Impact of Adverse Development Reinsurance Agreement (89)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,722 1,701 1,694 1,634 1,678 1,667        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 31                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,719 1,653 1,572 1,392 1,150 868 620 210    
Paid Impact of Adverse Development Reinsurance Agreement (51)                  
2014 | U.S. Other Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 32                  
Incurred Impact of Adverse Development Reinsurance Agreement (213) (245) (222) (276) (331) (296)        
2014 | U.S. Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,057 2,000 1,981 1,960 1,927 1,892 1,777 1,812    
Prior Year Development 2                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 57                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 174                  
Cumulative Number of Reported Claims 17,630                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (296)                  
IBNR Impact of Adverse Development Reinsurance Agreement (137)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,761 1,759 1,741 1,753 1,729 1,733        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 37                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,758 1,658 1,573 1,387 1,158 849 366 66    
Paid Impact of Adverse Development Reinsurance Agreement (79)                  
2014 | U.S. Financial Lines | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (55)                  
Incurred Impact of Adverse Development Reinsurance Agreement (296) (241) (240) (207) (198) (159)        
2014 | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,730 2,750 2,768 2,788 2,770 2,783 2,712 2,943    
Prior Year Development (12)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (20)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 65                  
Cumulative Number of Reported Claims | item 60,699                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (70)                  
IBNR Impact of Adverse Development Reinsurance Agreement (33)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 2,660 2,672 2,692 2,724 2,709 2,716        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 32                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 2,628 2,597 2,558 2,465 2,326 2,113 1,761 913    
Paid Impact of Adverse Development Reinsurance Agreement (13)                  
2014 | U.S. Property and Special Risks | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 8                  
Incurred Impact of Adverse Development Reinsurance Agreement (70) (78) (76) (64) (61) (67)        
2014 | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,587 1,588 1,584 1,583 1,572 1,572 1,562 1,552    
Prior Year Development (2)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (1)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 1                  
Cumulative Number of Reported Claims | item 275,040                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (5)                  
IBNR Impact of Adverse Development Reinsurance Agreement (1)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,582 1,584 1,580 1,571 1,564 1,564        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 0                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,572 1,568 1,555 1,536 1,507 1,463 1,380 959    
Paid Impact of Adverse Development Reinsurance Agreement (3)                  
2014 | U.S. Personal Insurance | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (1)                  
Incurred Impact of Adverse Development Reinsurance Agreement (5) (4) (4) (12) (8) (8)        
2014 | UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,141 1,100 1,156 1,069 1,029 1,065 1,041 1,066    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 41                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 67                  
Cumulative Number of Reported Claims | item 101,702                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 845 783 718 649 545 422 266 74    
2014 | UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,425 1,430 1,469 1,495 1,487 1,496 1,517 1,492    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (5)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ (5)                  
Cumulative Number of Reported Claims | item 48,480                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 1,386 1,373 1,363 1,335 1,296 1,225 938 322    
2014 | UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,662 2,664 2,663 2,664 2,671 2,674 2,692 2,682    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (2)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 3                  
Cumulative Number of Reported Claims | item 1,795,001                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 2,641 2,632 2,618 2,593 2,536 2,427 2,206 $ 1,464    
2015 | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,634 1,675 1,722 1,814 1,866 1,864 1,708      
Prior Year Development (64)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (41)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 421                  
Cumulative Number of Reported Claims | item 36,513                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (593)                  
IBNR Impact of Adverse Development Reinsurance Agreement (394)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,041 1,105 1,134 1,318 1,279 1,279        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 27                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,013 979 925 854 725 524 234      
Paid Impact of Adverse Development Reinsurance Agreement (24)                  
2015 | U.S. Workers Compensation | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (23)                  
Incurred Impact of Adverse Development Reinsurance Agreement (593) (570) (588) (496) (587) (585)        
2015 | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,721 1,694 1,656 1,603 1,440 1,463 989      
Prior Year Development 20                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 27                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 362                  
Cumulative Number of Reported Claims | item 2,922                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (490)                  
IBNR Impact of Adverse Development Reinsurance Agreement (248)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,231 1,211 1,163 1,139 1,015 1,027        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 114                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,124 1,061 935 718 391 210 9      
Paid Impact of Adverse Development Reinsurance Agreement (56)                  
2015 | U.S. Excess Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (7)                  
Incurred Impact of Adverse Development Reinsurance Agreement (490) (483) (493) (464) (425) (436)        
2015 | U.S. Other Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,824 1,834 1,794 1,736 1,829 1,762 1,329      
Prior Year Development 9                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (10)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 85                  
Cumulative Number of Reported Claims | item 35,309                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (262)                  
IBNR Impact of Adverse Development Reinsurance Agreement (61)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,562 1,553 1,493 1,423 1,373 1,361        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 24                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,603 1,485 1,351 1,087 769 309 105      
Paid Impact of Adverse Development Reinsurance Agreement (87)                  
2015 | U.S. Other Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 19                  
Incurred Impact of Adverse Development Reinsurance Agreement (262) (281) (301) (313) (456) (401)        
2015 | U.S. Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,959 1,874 1,830 1,788 1,743 1,762 1,737      
Prior Year Development 45                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 85                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 112                  
Cumulative Number of Reported Claims 16,223                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (364)                  
IBNR Impact of Adverse Development Reinsurance Agreement (101)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,595 1,550 1,552 1,462 1,430 1,429        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 11                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,686 1,488 1,282 1,055 791 390 63      
Paid Impact of Adverse Development Reinsurance Agreement (165)                  
2015 | U.S. Financial Lines | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (40)                  
Incurred Impact of Adverse Development Reinsurance Agreement (364) (324) (278) (326) (313) (333)        
2015 | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,868 2,860 2,865 2,901 2,911 2,982 3,100      
Prior Year Development 0                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 8                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 77                  
Cumulative Number of Reported Claims | item 59,363                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (107)                  
IBNR Impact of Adverse Development Reinsurance Agreement (47)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 2,761 2,761 2,771 2,814 2,813 2,841        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 30                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 2,726 2,688 2,618 2,492 2,237 1,871 1,037      
Paid Impact of Adverse Development Reinsurance Agreement (24)                  
2015 | U.S. Property and Special Risks | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development (8)                  
Incurred Impact of Adverse Development Reinsurance Agreement (107) (99) (94) (87) (98) (141)        
2015 | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,487 1,485 1,482 1,483 1,494 1,498 1,511      
Prior Year Development 2                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 2                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 10                  
Cumulative Number of Reported Claims | item 260,934                  
Incurred Impact of Adverse Development Reinsurance Agreement $ (5)                  
IBNR Impact of Adverse Development Reinsurance Agreement (2)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,482 1,480 1,476 1,472 1,475 1,476        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 8                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,463 1,461 1,455 1,439 1,411 1,320 931      
Paid Impact of Adverse Development Reinsurance Agreement (2)                  
2015 | U.S. Personal Insurance | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement (5) (5) (6) (11) (19) (22)        
2015 | UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,275 1,272 1,283 1,210 1,267 1,271 1,125      
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 3                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 93                  
Cumulative Number of Reported Claims | item 112,671                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 979 886 706 584 444 246 73      
2015 | UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,462 1,475 1,486 1,513 1,544 1,562 1,613      
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (13)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 13                  
Cumulative Number of Reported Claims | item 53,970                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 1,400 1,390 1,367 1,330 1,223 940 352      
2015 | UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,717 2,718 2,718 2,719 2,730 2,728 2,753      
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (1)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 6                  
Cumulative Number of Reported Claims | item 1,775,633                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 2,683 2,661 2,630 2,587 2,468 2,247 $ 1,486      
2016 | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,075 1,090 1,140 1,318 1,346 1,299        
Prior Year Development (15)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (15)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 293                  
Cumulative Number of Reported Claims | item 31,374                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,075 1,090 1,140 1,318 1,346 1,299        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 293                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 662 630 584 521 378 147        
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2016 | U.S. Workers Compensation | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0 0 0        
2016 | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,250 1,274 1,171 1,162 1,146 898        
Prior Year Development (24)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (24)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 436                  
Cumulative Number of Reported Claims | item 2,454                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,250 1,274 1,171 1,162 1,146 898        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 436                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 566 502 388 204 80 28        
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2016 | U.S. Excess Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0 0 0        
2016 | U.S. Other Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,323 1,340 1,391 1,321 1,343 1,339        
Prior Year Development (17)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (17)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 238                  
Cumulative Number of Reported Claims | item 28,646                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,323 1,340 1,391 1,321 1,343 1,339        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 238                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 938 846 703 489 298 77        
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2016 | U.S. Other Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0 0 0        
2016 | U.S. Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,281 2,139 2,064 1,993 1,855 1,605        
Prior Year Development 142                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 142                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 305                  
Cumulative Number of Reported Claims 16,111                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 2,281 2,139 2,064 1,993 1,855 1,605        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 305                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,826 1,659 1,358 1,002 499 73        
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2016 | U.S. Financial Lines | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0 0 0        
2016 | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 3,061 3,077 3,086 3,099 3,184 3,146        
Prior Year Development (16)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (16)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 38                  
Cumulative Number of Reported Claims | item 54,635                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 3,061 3,077 3,086 3,099 3,184 3,146        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 38                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 2,882 2,798 2,613 2,362 2,027 999        
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2016 | U.S. Property and Special Risks | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0 0 0        
2016 | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,544 1,542 1,540 1,533 1,533 1,536        
Prior Year Development 2                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 2                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 15                  
Cumulative Number of Reported Claims | item 247,133                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,544 1,542 1,540 1,533 1,533 1,536        
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 15                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,512 1,501 1,460 1,422 1,344 857        
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2016 | U.S. Personal Insurance | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0 0 0        
2016 | UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,640 1,643 1,540 1,538 1,483 1,351        
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (3)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 200                  
Cumulative Number of Reported Claims | item 140,787                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 1,086 955 795 602 389 123        
2016 | UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,716 1,720 1,724 1,722 1,729 1,581        
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (4)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 22                  
Cumulative Number of Reported Claims | item 56,996                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 1,610 1,581 1,534 1,396 1,138 467        
2016 | UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,668 2,673 2,674 2,682 2,698 2,703        
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (5)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 10                  
Cumulative Number of Reported Claims | item 1,797,359                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 2,616 2,587 2,532 2,427 2,211 $ 1,485        
2017 | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 731 763 776 850 789          
Prior Year Development (32)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (32)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 255                  
Cumulative Number of Reported Claims | item 27,125                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 731 763 776 850 789          
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 255                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 367 333 294 224 93          
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2017 | U.S. Workers Compensation | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0 0          
2017 | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,157 1,153 1,097 1,002 856          
Prior Year Development 4                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 4                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 371                  
Cumulative Number of Reported Claims | item 1,812                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,157 1,153 1,097 1,002 856          
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 371                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 585 505 156 45 1          
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2017 | U.S. Excess Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0 0          
2017 | U.S. Other Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 668 674 738 629 602          
Prior Year Development (6)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (6)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 115                  
Cumulative Number of Reported Claims | item 20,792                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 668 674 738 629 602          
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 115                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 455 314 216 111 51          
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2017 | U.S. Other Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0 0          
2017 | U.S. Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,898 1,846 1,756 1,675 1,564          
Prior Year Development 52                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 52                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 263                  
Cumulative Number of Reported Claims 15,149                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,898 1,846 1,756 1,675 1,564          
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 263                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,396 1,118 761 391 64          
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2017 | U.S. Financial Lines | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0 0          
2017 | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 4,749 4,740 4,742 4,902 5,368          
Prior Year Development 9                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 9                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 111                  
Cumulative Number of Reported Claims | item 79,437                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 4,749 4,740 4,742 4,902 5,368          
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 111                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 4,397 4,142 3,790 3,068 1,359          
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2017 | U.S. Property and Special Risks | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0 0          
2017 | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,924 2,057 2,011 2,137 1,878          
Prior Year Development (133)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (133)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 46                  
Cumulative Number of Reported Claims | item 219,420                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,924 2,057 2,011 2,137 1,878          
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 46                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,826 1,789 1,896 1,672 941          
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2017 | U.S. Personal Insurance | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0 0          
2017 | UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,419 1,356 1,289 1,359 1,334          
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 63                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 257                  
Cumulative Number of Reported Claims | item 148,004                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 774 619 460 288 100          
2017 | UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,639 1,656 1,650 1,659 1,702          
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (17)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 44                  
Cumulative Number of Reported Claims | item 53,464                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 1,458 1,400 1,252 965 360          
2017 | UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,533 2,536 2,541 2,559 2,643          
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (3)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 14                  
Cumulative Number of Reported Claims | item 1,722,818                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 2,479 2,437 2,353 2,164 $ 1,453          
2018 | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 911 961 1,021 998            
Prior Year Development (50)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (50)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 429                  
Cumulative Number of Reported Claims | item 21,739                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 911 961 1,021 998            
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 429                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 359 296 215 85            
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2018 | U.S. Workers Compensation | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0            
2018 | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 769 721 646 648            
Prior Year Development 48                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 48                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 288                  
Cumulative Number of Reported Claims | item 1,177                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 769 721 646 648            
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 288                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 315 227 125 1            
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2018 | U.S. Excess Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0            
2018 | U.S. Other Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 870 837 845 802            
Prior Year Development 33                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 33                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 355                  
Cumulative Number of Reported Claims | item 16,314                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 870 837 845 802            
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 355                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 360 227 122 43            
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2018 | U.S. Other Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0            
2018 | U.S. Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,063 1,882 1,766 1,640            
Prior Year Development 181                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 181                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 593                  
Cumulative Number of Reported Claims 14,721                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 2,063 1,882 1,766 1,640            
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 593                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,126 835 486 86            
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2018 | U.S. Financial Lines | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0            
2018 | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 3,930 3,712 3,757 3,702            
Prior Year Development 218                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 218                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 346                  
Cumulative Number of Reported Claims | item 69,199                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 3,930 3,712 3,757 3,702            
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 346                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 3,292 3,044 2,649 1,059            
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2018 | U.S. Property and Special Risks | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0            
2018 | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,937 2,154 2,193 2,188            
Prior Year Development (217)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (217)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 52                  
Cumulative Number of Reported Claims | item 101,536                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,937 2,154 2,193 2,188            
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 52                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,789 1,973 1,939 1,227            
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2018 | U.S. Personal Insurance | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0 0            
2018 | UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,551 1,521 1,452 1,379            
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 30                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 407                  
Cumulative Number of Reported Claims | item 151,608                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 760 586 383 116            
2018 | UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,545 1,555 1,580 1,570            
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (10)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 73                  
Cumulative Number of Reported Claims | item 44,018                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 1,324 1,194 1,002 323            
2018 | UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 3,055 3,055 3,050 3,137            
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 0                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 59                  
Cumulative Number of Reported Claims | item 1,885,145                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 2,885 2,781 2,577 $ 1,853            
2019 | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 812 873 887              
Prior Year Development (61)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (61)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 359                  
Cumulative Number of Reported Claims | item 16,471                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 812 873 887              
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 359                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 301 219 93              
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2019 | U.S. Workers Compensation | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0              
2019 | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 597 583 577              
Prior Year Development 14                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 14                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 392                  
Cumulative Number of Reported Claims | item 998,000,000                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 597 583 577              
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 392                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 79 43 7              
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2019 | U.S. Excess Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0              
2019 | U.S. Other Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,053 1,058 1,059              
Prior Year Development (5)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (5)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 683                  
Cumulative Number of Reported Claims | item 19,976                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,053 1,058 1,059              
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 683                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 226 138 53              
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2019 | U.S. Other Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0              
2019 | U.S. Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,627 1,536 1,503              
Prior Year Development 91                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 91                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 637                  
Cumulative Number of Reported Claims 13,122                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,627 1,536 1,503              
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 637                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 642 367 94              
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2019 | U.S. Financial Lines | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0              
2019 | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,882 2,850 2,809              
Prior Year Development 32                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 32                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 300                  
Cumulative Number of Reported Claims | item 78,109                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 2,882 2,850 2,809              
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 300                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 2,341 2,032 1,137              
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2019 | U.S. Property and Special Risks | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0              
2019 | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,646 1,664 1,593              
Prior Year Development (18)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (18)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 185                  
Cumulative Number of Reported Claims | item 91,463                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,646 1,664 1,593              
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 185                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,379 1,295 884              
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2019 | U.S. Personal Insurance | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0 0              
2019 | UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,372 1,296 1,483              
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 76                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 543                  
Cumulative Number of Reported Claims | item 139,801                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 490 323 101              
2019 | UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,143 1,148 1,206              
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (5)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 121                  
Cumulative Number of Reported Claims | item 32,749                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 840 666 272              
2019 | UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,473 2,474 2,521              
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (1)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 89                  
Cumulative Number of Reported Claims | item 1,656,951                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 2,247 2,090 $ 1,454              
2020 | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 573 597                
Prior Year Development (24)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (24)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 276                  
Cumulative Number of Reported Claims | item 13,245                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 573 597                
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 276                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 159 64                
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2020 | U.S. Workers Compensation | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0                
2020 | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 413 406                
Prior Year Development 7                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 7                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 371                  
Cumulative Number of Reported Claims | item 790                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 413 406                
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 371                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 15 4                
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2020 | U.S. Excess Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0                
2020 | U.S. Other Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 576 524                
Prior Year Development 52                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 52                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 427                  
Cumulative Number of Reported Claims | item 9,958                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 576 524                
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 427                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 73 26                
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2020 | U.S. Other Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0                
2020 | U.S. Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,252 1,213                
Prior Year Development 39                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 39                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 685                  
Cumulative Number of Reported Claims 10,055                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,252 1,213                
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 685                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 356 84                
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2020 | U.S. Financial Lines | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0                
2020 | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 4,466 4,481                
Prior Year Development (15)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (15)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 1,293                  
Cumulative Number of Reported Claims | item 66,812                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 4,466 4,481                
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 1,293                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 2,356 1,180                
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2020 | U.S. Property and Special Risks | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0                
2020 | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 906 954                
Prior Year Development (48)                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (48)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 155                  
Cumulative Number of Reported Claims | item 52,251                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 906 954                
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 155                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 679 667                
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2020 | U.S. Personal Insurance | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0 0                
2020 | UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,303 1,253                
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 50                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 834                  
Cumulative Number of Reported Claims | item 86,834                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 233 61                
2020 | UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,278 1,329                
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (51)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 281                  
Cumulative Number of Reported Claims | item 24,220                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 688 257                
2020 | UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,104 2,252                
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (148)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 141                  
Cumulative Number of Reported Claims | item 1,354,093                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 1,746 $ 1,212                
2021 | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 597                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 446                  
Cumulative Number of Reported Claims | item 9,067                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 597                  
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 446                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 60                  
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2021 | U.S. Workers Compensation | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0                  
2021 | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 278                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 245                  
Cumulative Number of Reported Claims | item 340                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 278                  
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 245                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 4                  
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2021 | U.S. Excess Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0                  
2021 | U.S. Other Casualty                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 795                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 711                  
Cumulative Number of Reported Claims | item 7,561                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 795                  
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 711                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 32                  
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2021 | U.S. Other Casualty | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0                  
2021 | U.S. Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,430                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 1,318                  
Cumulative Number of Reported Claims 6,386                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 1,430                  
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 1,318                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 43                  
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2021 | U.S. Financial Lines | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0                  
2021 | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 3,554                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 1,316                  
Cumulative Number of Reported Claims | item 55,054                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 3,554                  
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 1,316                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 1,174                  
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2021 | U.S. Property and Special Risks | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0                  
2021 | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 748                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 129                  
Cumulative Number of Reported Claims | item 40,437                  
Incurred Impact of Adverse Development Reinsurance Agreement $ 0                  
IBNR Impact of Adverse Development Reinsurance Agreement 0                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) 748                  
Total of IBNR Liabilities Net of Impact Adverse Development Reinsurance Agreement 129                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 488                  
Paid Impact of Adverse Development Reinsurance Agreement 0                  
2021 | U.S. Personal Insurance | Adverse Development Reinsurance                    
Claims Development [Line Items]                    
Prior Year Development 0                  
Incurred Impact of Adverse Development Reinsurance Agreement 0                  
2021 | UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,557                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 1,204                  
Cumulative Number of Reported Claims | item 62,310                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 53                  
2021 | UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 1,223                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 444                  
Cumulative Number of Reported Claims | item 14,493                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 194                  
2021 | UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
Incurred Losses and Allocated Loss Adjustment Expenses, Undiscounted and Net of Reinsurance 2,171                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 388                  
Cumulative Number of Reported Claims | item 1,197,412                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance $ 1,188                  
Unallocated | U.S. Workers Compensation                    
Claims Development [Line Items]                    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 28                  
Unallocated | U.S. Excess Casualty                    
Claims Development [Line Items]                    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 13                  
Unallocated | U.S. Other Casualty                    
Claims Development [Line Items]                    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (19)                  
Unallocated | U.S. Financial Lines                    
Claims Development [Line Items]                    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 45                  
Unallocated | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement (13)                  
Unallocated | U.S. Personal Insurance                    
Claims Development [Line Items]                    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 0                  
Unallocated | UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 0                  
Unallocated | UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 0                  
Unallocated | UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement 0                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 0                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 0                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement | U.S. Other Casualty                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 0                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement | U.S. Financial Lines                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 0                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 0                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 0                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement | UK/Europe Casualty and Financial Lines                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 0                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement | UK/Europe Property and Special Risks                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 0                  
2021 Prior Year Development Excluding the Impact of Adverse Development Reinsurance Agreement | UK/Europe and Japan Personal Insurance                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 0                  
Incurred Impact of Adverse Development Reinsurance Agreement | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 126                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (3,570)                  
Incurred Impact of Adverse Development Reinsurance Agreement | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 129                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (1,680)                  
Incurred Impact of Adverse Development Reinsurance Agreement | U.S. Other Casualty                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 177                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (1,000)                  
Incurred Impact of Adverse Development Reinsurance Agreement | U.S. Financial Lines                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 326                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (182)                  
Incurred Impact of Adverse Development Reinsurance Agreement | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 47                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (126)                  
Incurred Impact of Adverse Development Reinsurance Agreement | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 6                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (5)                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 7,160                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance 1,065                  
Unallocated Loss Adjustment Expense Prior Year Development (70)                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 4,158                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Total 8,746                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 5,412                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance 516                  
Unallocated Loss Adjustment Expense Prior Year Development 92                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 3,850                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) | U.S. Other Casualty                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 9,259                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance 435                  
Unallocated Loss Adjustment Expense Prior Year Development 28                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 3,805                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) | U.S. Financial Lines                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 11,872                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (44)                  
Unallocated Loss Adjustment Expense Prior Year Development 60                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 5,356                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 28,308                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance 214                  
Unallocated Loss Adjustment Expense Prior Year Development (6)                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 6,615                  
2021 (Net of Impact of Adverse Development Reinsurance Agreement) | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance 14,576                  
Liabilities for losses and loss adjustment expenses and prior year development before 2012, net of reinsurance (67)                  
Unallocated Loss Adjustment Expense Prior Year Development 0                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 1,001                  
Paid Impact of Adverse Development Reinsurance Agreement | U.S. Workers Compensation                    
Claims Development [Line Items]                    
Paid Impact of Adverse Development Reinsurance Agreement (126)                  
Paid Impact of Adverse Development Reinsurance Agreement | U.S. Excess Casualty                    
Claims Development [Line Items]                    
Paid Impact of Adverse Development Reinsurance Agreement (129)                  
Paid Impact of Adverse Development Reinsurance Agreement | U.S. Other Casualty                    
Claims Development [Line Items]                    
Paid Impact of Adverse Development Reinsurance Agreement (177)                  
Paid Impact of Adverse Development Reinsurance Agreement | U.S. Financial Lines                    
Claims Development [Line Items]                    
Paid Impact of Adverse Development Reinsurance Agreement (326)                  
Paid Impact of Adverse Development Reinsurance Agreement | U.S. Property and Special Risks                    
Claims Development [Line Items]                    
Paid Impact of Adverse Development Reinsurance Agreement (47)                  
Paid Impact of Adverse Development Reinsurance Agreement | U.S. Personal Insurance                    
Claims Development [Line Items]                    
Paid Impact of Adverse Development Reinsurance Agreement $ (6)