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Insurance Claim Reserves (Details) - Claim Development
$ in Millions
Dec. 31, 2020
USD ($)
claims
Dec. 31, 2019
USD ($)
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 ($)
Dec. 31, 2011
USD ($)
Claims Development                    
Total net liability (Audited) $ 47,434                  
Property-casualty [Member]                    
Claims Development                    
Total net liability (Audited) 47,434                  
Business Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 11,646                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 6,171                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 5,475                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 2,963                  
Total net liability (Audited) 8,438                  
Business Insurance [Member] | Commercial property [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 5,152                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 4,392                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 760                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 119                  
Total net liability (Audited) 879                  
Business Insurance [Member] | Commercial multi-peril [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 18,784                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 14,960                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 3,824                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 285                  
Total net liability (Audited) 4,109                  
Business Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 8,423                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 5,021                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 3,402                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 205                  
Total net liability (Audited) 3,607                  
Business Insurance [Member] | Workers' compensation [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 24,351                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 13,519                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 10,832                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 5,622                  
Total net liability (Audited) 16,454                  
Bond & Specialty Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 5,541                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 3,437                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 2,104                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 44                  
Total net liability (Audited) 2,148                  
Bond & Specialty Insurance [Member] | Fidelity and surety [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,143                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 752                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 391                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 48                  
Total net liability (Audited) 439                  
Personal Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 15,374                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 12,833                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 2,541                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 227                  
Total net liability (Audited) 2,768                  
Personal Insurance [Member] | Homeowners (excluding Other) [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 11,420                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 10,031                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 1,389                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 16                  
Total net liability (Audited) 1,405                  
Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 4,118                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 3,410                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 708                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 29                  
Total net liability (Audited) 737                  
Short-duration Insurance Contracts, Accident Year 2011 [Member] | Business Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 920 $ 922 $ 908 $ 913 $ 935 $ 972 $ 998 $ 1,065 $ 1,074 $ 1,004
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 826 819 799 762 725 660 539 355 187 47
IBNR Reserves Dec. 31, 2020 (Audited) $ 64                  
Cumulative Number of Reported Claims (Audited) | claims 27,636                  
Short-duration Insurance Contracts, Accident Year 2011 [Member] | Business Insurance [Member] | Commercial multi-peril [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,272 2,272 2,279 2,283 2,287 2,296 2,286 2,269 2,244 2,235
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 2,239 2,234 2,222 2,193 2,156 2,088 1,979 1,803 1,573 1,060
IBNR Reserves Dec. 31, 2020 (Audited) $ 24                  
Cumulative Number of Reported Claims (Audited) | claims 125,994                  
Short-duration Insurance Contracts, Accident Year 2011 [Member] | Business Insurance [Member] | Workers' compensation [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,295 2,320 2,348 2,363 2,385 2,379 2,350 2,347 2,303 2,284
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,757 1,732 1,696 1,652 1,583 1,487 1,365 1,185 911 420
IBNR Reserves Dec. 31, 2020 (Audited) $ 285                  
Cumulative Number of Reported Claims (Audited) | claims 137,116                  
Short-duration Insurance Contracts, Accident Year 2011 [Member] | Bond & Specialty Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 504 506 508 520 545 601 632 639 596 565
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 501 496 490 476 447 414 324 249 143 33
IBNR Reserves Dec. 31, 2020 (Audited) $ 2                  
Cumulative Number of Reported Claims (Audited) | claims 5,219                  
Short-duration Insurance Contracts, Accident Year 2011 [Member] | Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 415 414 424 429 434 441 449 453 445 467
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 412 408 404 396 377 355 319 285 253 $ 179
IBNR Reserves Dec. 31, 2020 (Audited) $ (2)                  
Cumulative Number of Reported Claims (Audited) | claims 55,789                  
Short-duration Insurance Contracts, Accident Year 2012 [Member] | Business Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 941 920 917 905 892 913 935 985 989  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 831 811 754 699 589 489 295 150 32  
IBNR Reserves Dec. 31, 2020 (Audited) $ 77                  
Cumulative Number of Reported Claims (Audited) | claims 24,995                  
Short-duration Insurance Contracts, Accident Year 2012 [Member] | Business Insurance [Member] | Commercial multi-peril [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,853 1,854 1,859 1,867 1,888 1,888 1,903 1,883 1,885  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,811 1,804 1,780 1,752 1,699 1,590 1,424 1,246 795  
IBNR Reserves Dec. 31, 2020 (Audited) $ 31                  
Cumulative Number of Reported Claims (Audited) | claims 104,964                  
Short-duration Insurance Contracts, Accident Year 2012 [Member] | Business Insurance [Member] | Workers' compensation [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,377 2,387 2,416 2,453 2,445 2,456 2,457 2,456 2,447  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,768 1,735 1,689 1,629 1,536 1,394 1,217 940 443  
IBNR Reserves Dec. 31, 2020 (Audited) $ 340                  
Cumulative Number of Reported Claims (Audited) | claims 138,346                  
Short-duration Insurance Contracts, Accident Year 2012 [Member] | Bond & Specialty Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 581 593 605 599 601 605 614 591 538  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 459 453 436 419 383 342 255 160 38  
IBNR Reserves Dec. 31, 2020 (Audited) $ 7                  
Cumulative Number of Reported Claims (Audited) | claims 4,869                  
Short-duration Insurance Contracts, Accident Year 2012 [Member] | Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 368 368 380 386 403 404 421 420 442  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 359 353 348 339 321 292 266 235 $ 168  
IBNR Reserves Dec. 31, 2020 (Audited) $ 1                  
Cumulative Number of Reported Claims (Audited) | claims 51,227                  
Short-duration Insurance Contracts, Accident Year 2013 [Member] | Business Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 975 975 933 927 940 958 975 965    
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 836 816 745 639 498 363 175 35    
IBNR Reserves Dec. 31, 2020 (Audited) $ 92                  
Cumulative Number of Reported Claims (Audited) | claims 22,711                  
Short-duration Insurance Contracts, Accident Year 2013 [Member] | Business Insurance [Member] | Commercial multi-peril [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,598 1,599 1,600 1,591 1,609 1,620 1,623 1,615    
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,532 1,516 1,475 1,410 1,304 1,167 987 644    
IBNR Reserves Dec. 31, 2020 (Audited) $ 31                  
Cumulative Number of Reported Claims (Audited) | claims 83,921                  
Short-duration Insurance Contracts, Accident Year 2013 [Member] | Business Insurance [Member] | Workers' compensation [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,321 2,354 2,423 2,463 2,506 2,540 2,545 2,553    
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,700 1,659 1,604 1,525 1,413 1,237 954 458    
IBNR Reserves Dec. 31, 2020 (Audited) $ 367                  
Cumulative Number of Reported Claims (Audited) | claims 134,518                  
Short-duration Insurance Contracts, Accident Year 2013 [Member] | Bond & Specialty Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 575 586 607 654 630 606 565 510    
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 462 451 434 400 352 252 154 34    
IBNR Reserves Dec. 31, 2020 (Audited) $ 3                  
Cumulative Number of Reported Claims (Audited) | claims 4,465                  
Short-duration Insurance Contracts, Accident Year 2013 [Member] | Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 435 440 450 452 465 477 486 493    
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 420 411 394 375 342 309 276 $ 197    
IBNR Reserves Dec. 31, 2020 (Audited) $ (4)                  
Cumulative Number of Reported Claims (Audited) | claims 54,237                  
Short-duration Insurance Contracts, Accident Year 2014 [Member] | Business Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 988 1,013 956 948 983 989 976      
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 805 750 640 515 321 163 37      
IBNR Reserves Dec. 31, 2020 (Audited) $ 127                  
Cumulative Number of Reported Claims (Audited) | claims 22,465                  
Short-duration Insurance Contracts, Accident Year 2014 [Member] | Business Insurance [Member] | Commercial multi-peril [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,627 1,627 1,626 1,617 1,625 1,627 1,663      
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,544 1,512 1,448 1,328 1,154 956 628      
IBNR Reserves Dec. 31, 2020 (Audited) $ 41                  
Cumulative Number of Reported Claims (Audited) | claims 78,388                  
Short-duration Insurance Contracts, Accident Year 2014 [Member] | Business Insurance [Member] | Workers' compensation [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,352 2,393 2,430 2,476 2,547 2,553 2,554      
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,634 1,581 1,505 1,399 1,224 944 455      
IBNR Reserves Dec. 31, 2020 (Audited) $ 434                  
Cumulative Number of Reported Claims (Audited) | claims 131,355                  
Short-duration Insurance Contracts, Accident Year 2014 [Member] | Bond & Specialty Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 450 452 473 518 563 571 549      
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 418 407 367 312 239 150 38      
IBNR Reserves Dec. 31, 2020 (Audited) $ 18                  
Cumulative Number of Reported Claims (Audited) | claims 4,367                  
Short-duration Insurance Contracts, Accident Year 2014 [Member] | Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 430 430 433 440 452 452 436      
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 407 390 368 336 307 270 $ 193      
IBNR Reserves Dec. 31, 2020 (Audited) $ (6)                  
Cumulative Number of Reported Claims (Audited) | claims 52,290                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Business Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,087 1,057 967 923 956 998        
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 828 740 558 336 137 36        
IBNR Reserves Dec. 31, 2020 (Audited) $ 145                  
Cumulative Number of Reported Claims (Audited) | claims 21,531                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Business Insurance [Member] | Commercial multi-peril [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,593 1,606 1,597 1,593 1,625 1,568        
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,452 1,409 1,310 1,144 970 595        
IBNR Reserves Dec. 31, 2020 (Audited) $ 64                  
Cumulative Number of Reported Claims (Audited) | claims 71,812                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Business Insurance [Member] | Workers' compensation [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,279 2,372 2,441 2,505 2,585 2,644        
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,470 1,411 1,310 1,154 893 430        
IBNR Reserves Dec. 31, 2020 (Audited) $ 511                  
Cumulative Number of Reported Claims (Audited) | claims 128,939                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Bond & Specialty Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 414 395 437 486 524 528        
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 348 338 310 234 141 38        
IBNR Reserves Dec. 31, 2020 (Audited) $ 35                  
Cumulative Number of Reported Claims (Audited) | claims 4,217                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 363 363 362 366 366 366        
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 327 312 287 258 230 $ 164        
IBNR Reserves Dec. 31, 2020 (Audited) $ 7                  
Cumulative Number of Reported Claims (Audited) | claims 45,205                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Business Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,204 1,187 1,087 1,058 1,075          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 758 649 421 191 35          
IBNR Reserves Dec. 31, 2020 (Audited) $ 281                  
Cumulative Number of Reported Claims (Audited) | claims 20,325                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Business Insurance [Member] | Commercial property [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 813 809 820 863 896          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 780 767 745 685 441          
IBNR Reserves Dec. 31, 2020 (Audited) $ 14                  
Cumulative Number of Reported Claims (Audited) | claims 22,337                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Business Insurance [Member] | Commercial multi-peril [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,601 1,590 1,598 1,623 1,662          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,373 1,278 1,133 950 585          
IBNR Reserves Dec. 31, 2020 (Audited) $ 95                  
Cumulative Number of Reported Claims (Audited) | claims 69,213                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Business Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,417 1,409 1,371 1,303 1,278          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,265 1,158 931 688 412          
IBNR Reserves Dec. 31, 2020 (Audited) $ 52                  
Cumulative Number of Reported Claims (Audited) | claims 183,313                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Business Insurance [Member] | Workers' compensation [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,372 2,473 2,569 2,690 2,768          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,367 1,272 1,118 873 421          
IBNR Reserves Dec. 31, 2020 (Audited) $ 569                  
Cumulative Number of Reported Claims (Audited) | claims 123,652                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Bond & Specialty Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 514 520 504 511 512          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 378 313 233 141 30          
IBNR Reserves Dec. 31, 2020 (Audited) $ 53                  
Cumulative Number of Reported Claims (Audited) | claims 4,371                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Bond & Specialty Insurance [Member] | Fidelity and surety [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 215 208 205 239 226          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 174 149 142 121 54          
IBNR Reserves Dec. 31, 2020 (Audited) $ 13                  
Cumulative Number of Reported Claims (Audited) | claims 892                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Personal Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,745 2,752 2,772 2,791 2,779          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 2,686 2,616 2,466 2,203 1,610          
IBNR Reserves Dec. 31, 2020 (Audited) $ 14                  
Cumulative Number of Reported Claims (Audited) | claims 922,219                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Personal Insurance [Member] | Homeowners (excluding Other) [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,506 1,511 1,525 1,547 1,556          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,489 1,479 1,455 1,392 1,049          
IBNR Reserves Dec. 31, 2020 (Audited) $ 5                  
Cumulative Number of Reported Claims (Audited) | claims 144,534                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 426 426 416 416 367          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 373 349 315 288 $ 215          
IBNR Reserves Dec. 31, 2020 (Audited) $ 8                  
Cumulative Number of Reported Claims (Audited) | claims 45,759                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Business Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,234 1,196 1,143 1,133            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 552 378 180 40            
IBNR Reserves Dec. 31, 2020 (Audited) $ 410                  
Cumulative Number of Reported Claims (Audited) | claims 18,736                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Business Insurance [Member] | Commercial property [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,128 1,151 1,177 1,209            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,094 1,073 1,003 618            
IBNR Reserves Dec. 31, 2020 (Audited) $ 4                  
Cumulative Number of Reported Claims (Audited) | claims 25,121                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Business Insurance [Member] | Commercial multi-peril [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,919 1,956 1,928 1,872            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,531 1,388 1,199 716            
IBNR Reserves Dec. 31, 2020 (Audited) $ 132                  
Cumulative Number of Reported Claims (Audited) | claims 71,967                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Business Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,522 1,524 1,501 1,386            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,226 1,027 746 456            
IBNR Reserves Dec. 31, 2020 (Audited) $ 113                  
Cumulative Number of Reported Claims (Audited) | claims 191,931                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Business Insurance [Member] | Workers' compensation [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,483 2,584 2,681 2,779            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,314 1,154 890 433            
IBNR Reserves Dec. 31, 2020 (Audited) $ 729                  
Cumulative Number of Reported Claims (Audited) | claims 121,345                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Bond & Specialty Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 493 526 517 534            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 340 262 155 38            
IBNR Reserves Dec. 31, 2020 (Audited) $ 69                  
Cumulative Number of Reported Claims (Audited) | claims 4,544                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Bond & Specialty Insurance [Member] | Fidelity and surety [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 241 240 271 244            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 205 194 166 70            
IBNR Reserves Dec. 31, 2020 (Audited) $ 21                  
Cumulative Number of Reported Claims (Audited) | claims 926                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Personal Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 3,206 3,221 3,256 3,323            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 3,046 2,887 2,575 1,912            
IBNR Reserves Dec. 31, 2020 (Audited) $ 57                  
Cumulative Number of Reported Claims (Audited) | claims 1,062,577                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Personal Insurance [Member] | Homeowners (excluding Other) [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,170 2,343 2,340 2,312            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 2,089 2,197 2,059 1,471            
IBNR Reserves Dec. 31, 2020 (Audited) $ 27                  
Cumulative Number of Reported Claims (Audited) | claims 170,114                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 410 410 387 352            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 326 301 261 $ 185            
IBNR Reserves Dec. 31, 2020 (Audited) $ 16                  
Cumulative Number of Reported Claims (Audited) | claims 46,808                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | Business Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,344 1,312 1,253              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 441 202 42              
IBNR Reserves Dec. 31, 2020 (Audited) $ 588                  
Cumulative Number of Reported Claims (Audited) | claims 18,200                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | Business Insurance [Member] | Commercial property [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,070 1,079 1,093              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 981 928 561              
IBNR Reserves Dec. 31, 2020 (Audited) $ 25                  
Cumulative Number of Reported Claims (Audited) | claims 25,013                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | Business Insurance [Member] | Commercial multi-peril [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,092 2,114 1,976              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,500 1,302 792              
IBNR Reserves Dec. 31, 2020 (Audited) $ 245                  
Cumulative Number of Reported Claims (Audited) | claims 69,513                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | Business Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,745 1,742 1,645              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,159 848 515              
IBNR Reserves Dec. 31, 2020 (Audited) $ 251                  
Cumulative Number of Reported Claims (Audited) | claims 204,098                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | Business Insurance [Member] | Workers' compensation [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,599 2,687 2,744              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,169 919 440              
IBNR Reserves Dec. 31, 2020 (Audited) $ 922                  
Cumulative Number of Reported Claims (Audited) | claims 122,416                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | Bond & Specialty Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 585 548 530              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 290 182 49              
IBNR Reserves Dec. 31, 2020 (Audited) $ 150                  
Cumulative Number of Reported Claims (Audited) | claims 4,693                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | Bond & Specialty Insurance [Member] | Fidelity and surety [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 220 235 220              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 202 171 64              
IBNR Reserves Dec. 31, 2020 (Audited) $ 1                  
Cumulative Number of Reported Claims (Audited) | claims 886                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | Personal Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 3,233 3,269 3,281              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 2,880 2,582 1,889              
IBNR Reserves Dec. 31, 2020 (Audited) $ 155                  
Cumulative Number of Reported Claims (Audited) | claims 1,050,608                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | Personal Insurance [Member] | Homeowners (excluding Other) [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,381 2,574 2,610              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 2,255 2,298 1,657              
IBNR Reserves Dec. 31, 2020 (Audited) $ 32                  
Cumulative Number of Reported Claims (Audited) | claims 187,093                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 471 469 447              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 346 310 $ 222              
IBNR Reserves Dec. 31, 2020 (Audited) $ 33                  
Cumulative Number of Reported Claims (Audited) | claims 50,558                  
Short-duration Insurance Contracts, Accident Year 2019 [Member] | Business Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,486 1,447                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 233 51                
IBNR Reserves Dec. 31, 2020 (Audited) $ 933                  
Cumulative Number of Reported Claims (Audited) | claims 16,060                  
Short-duration Insurance Contracts, Accident Year 2019 [Member] | Business Insurance [Member] | Commercial property [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,034 1,069                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 957 610                
IBNR Reserves Dec. 31, 2020 (Audited) $ (6)                  
Cumulative Number of Reported Claims (Audited) | claims 25,185                  
Short-duration Insurance Contracts, Accident Year 2019 [Member] | Business Insurance [Member] | Commercial multi-peril [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,087 2,017                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,187 707                
IBNR Reserves Dec. 31, 2020 (Audited) $ 467                  
Cumulative Number of Reported Claims (Audited) | claims 64,425                  
Short-duration Insurance Contracts, Accident Year 2019 [Member] | Business Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,951 1,835                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 934 539                
IBNR Reserves Dec. 31, 2020 (Audited) $ 547                  
Cumulative Number of Reported Claims (Audited) | claims 205,355                  
Short-duration Insurance Contracts, Accident Year 2019 [Member] | Business Insurance [Member] | Workers' compensation [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,714 2,680                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 951 466                
IBNR Reserves Dec. 31, 2020 (Audited) $ 1,023                  
Cumulative Number of Reported Claims (Audited) | claims 118,868                  
Short-duration Insurance Contracts, Accident Year 2019 [Member] | Bond & Specialty Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 653 588                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 189 51                
IBNR Reserves Dec. 31, 2020 (Audited) $ 317                  
Cumulative Number of Reported Claims (Audited) | claims 4,992                  
Short-duration Insurance Contracts, Accident Year 2019 [Member] | Bond & Specialty Insurance [Member] | Fidelity and surety [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 193 203                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 121 49                
IBNR Reserves Dec. 31, 2020 (Audited) $ 45                  
Cumulative Number of Reported Claims (Audited) | claims 827                  
Short-duration Insurance Contracts, Accident Year 2019 [Member] | Personal Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 3,361 3,362                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 2,650 1,933                
IBNR Reserves Dec. 31, 2020 (Audited) $ 368                  
Cumulative Number of Reported Claims (Audited) | claims 1,029,935                  
Short-duration Insurance Contracts, Accident Year 2019 [Member] | Personal Insurance [Member] | Homeowners (excluding Other) [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,344 2,297                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 2,179 1,613                
IBNR Reserves Dec. 31, 2020 (Audited) $ 65                  
Cumulative Number of Reported Claims (Audited) | claims 179,977                  
Short-duration Insurance Contracts, Accident Year 2019 [Member] | Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 447 452                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 294 $ 219                
IBNR Reserves Dec. 31, 2020 (Audited) $ 60                  
Cumulative Number of Reported Claims (Audited) | claims 47,945                  
Short-duration Insurance Contracts, Accident Year 2020 [Member] | Business Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,467                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 61                  
IBNR Reserves Dec. 31, 2020 (Audited) $ 1,268                  
Cumulative Number of Reported Claims (Audited) | claims 8,637                  
Short-duration Insurance Contracts, Accident Year 2020 [Member] | Business Insurance [Member] | Commercial property [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,107                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 580                  
IBNR Reserves Dec. 31, 2020 (Audited) $ 160                  
Cumulative Number of Reported Claims (Audited) | claims 22,387                  
Short-duration Insurance Contracts, Accident Year 2020 [Member] | Business Insurance [Member] | Commercial multi-peril [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,142                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 791                  
IBNR Reserves Dec. 31, 2020 (Audited) $ 856                  
Cumulative Number of Reported Claims (Audited) | claims 59,815                  
Short-duration Insurance Contracts, Accident Year 2020 [Member] | Business Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 1,788                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 437                  
IBNR Reserves Dec. 31, 2020 (Audited) $ 1,036                  
Cumulative Number of Reported Claims (Audited) | claims 130,725                  
Short-duration Insurance Contracts, Accident Year 2020 [Member] | Business Insurance [Member] | Workers' compensation [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,559                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 389                  
IBNR Reserves Dec. 31, 2020 (Audited) $ 1,690                  
Cumulative Number of Reported Claims (Audited) | claims 86,459                  
Short-duration Insurance Contracts, Accident Year 2020 [Member] | Bond & Specialty Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 772                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 52                  
IBNR Reserves Dec. 31, 2020 (Audited) $ 598                  
Cumulative Number of Reported Claims (Audited) | claims 3,450                  
Short-duration Insurance Contracts, Accident Year 2020 [Member] | Bond & Specialty Insurance [Member] | Fidelity and surety [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 274                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 50                  
IBNR Reserves Dec. 31, 2020 (Audited) $ 189                  
Cumulative Number of Reported Claims (Audited) | claims 580                  
Short-duration Insurance Contracts, Accident Year 2020 [Member] | Personal Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 2,829                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 1,571                  
IBNR Reserves Dec. 31, 2020 (Audited) $ 807                  
Cumulative Number of Reported Claims (Audited) | claims 741,369                  
Short-duration Insurance Contracts, Accident Year 2020 [Member] | Personal Insurance [Member] | Homeowners (excluding Other) [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 3,019                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 2,019                  
IBNR Reserves Dec. 31, 2020 (Audited) $ 737                  
Cumulative Number of Reported Claims (Audited) | claims 192,501                  
Short-duration Insurance Contracts, Accident Year 2020 [Member] | Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) $ 353                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2020) 146                  
IBNR Reserves Dec. 31, 2020 (Audited) $ 132                  
Cumulative Number of Reported Claims (Audited) | claims 28,763