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Insurance Claim Reserves (Details) - Claim Development
$ in Millions
Dec. 31, 2019
USD ($)
item
Dec. 31, 2018
USD ($)
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 ($)
Dec. 31, 2010
USD ($)
Claims Development                    
Total net liability (Audited) $ 44,889                  
Property-casualty [Member]                    
Claims Development                    
Total net liability (Audited) 44,889                  
Business Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 10,929                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 6,030                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 4,899                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 2,850                  
Total net liability (Audited) 7,749                  
Business Insurance [Member] | Commercial property [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 4,845                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 4,095                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 750                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 137                  
Total net liability (Audited) 887                  
Business Insurance [Member] | Commercial multi-peril [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 18,503                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 14,990                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 3,513                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 271                  
Total net liability (Audited) 3,784                  
Business Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 7,808                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 4,753                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 3,055                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 182                  
Total net liability (Audited) 3,237                  
Business Insurance [Member] | Workers' compensation [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 24,234                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 13,419                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 10,815                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 5,369                  
Total net liability (Audited) 16,184                  
Bond & Specialty Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 5,374                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 3,588                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 1,786                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 38                  
Total net liability (Audited) 1,824                  
Bond & Specialty Insurance [Member] | Fidelity and surety [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,023                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 651                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 372                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 27                  
Total net liability (Audited) 399                  
Personal Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 14,823                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 12,192                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 2,631                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 231                  
Total net liability (Audited) 2,862                  
Personal Insurance [Member] | Homeowners (excluding Other) [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 10,168                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 9,016                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 1,152                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 16                  
Total net liability (Audited) 1,168                  
Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 4,190                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 3,472                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Disclosed Accident Years (Audited) 718                  
Liability for Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Before Disclosed Accident Years (Audited) 21                  
Total net liability (Audited) 739                  
Short-duration Insurance Contracts, Accident Year 2010 [Member] | Business Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 900 $ 911 $ 908 $ 918 $ 912 $ 927 $ 959 $ 1,021 $ 1,031 $ 1,028
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 814 800 781 756 702 629 487 324 139 35
IBNR Reserves Dec. 31, 2019 (Audited) $ 62                  
Cumulative Number of Reported Claims (Audited) | item 27,993                  
Short-duration Insurance Contracts, Accident Year 2010 [Member] | Business Insurance [Member] | Commercial multi-peril [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) $ 1,868 1,881 1,885 1,898 1,892 1,895 1,861 1,832 1,826 1,711
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,840 1,834 1,819 1,798 1,763 1,698 1,579 1,395 1,180 709
IBNR Reserves Dec. 31, 2019 (Audited) $ 19                  
Cumulative Number of Reported Claims (Audited) | item 112,074                  
Short-duration Insurance Contracts, Accident Year 2010 [Member] | Business Insurance [Member] | Workers' compensation [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) $ 1,984 2,003 2,021 2,055 2,052 2,049 2,056 2,035 2,042 1,886
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,490 1,465 1,430 1,385 1,321 1,246 1,133 978 750 341
IBNR Reserves Dec. 31, 2019 (Audited) $ 248                  
Cumulative Number of Reported Claims (Audited) | item 117,466                  
Short-duration Insurance Contracts, Accident Year 2010 [Member] | Bond & Specialty Insurance [Member] | General liability [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) $ 660 657 653 653 668 661 679 679 612 571
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 635 631 623 597 565 482 396 291 152 33
IBNR Reserves Dec. 31, 2019 (Audited) $ 16                  
Cumulative Number of Reported Claims (Audited) | item 5,677                  
Short-duration Insurance Contracts, Accident Year 2010 [Member] | Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) $ 477 481 482 489 493 501 514 499 488 487
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 468 465 459 447 430 400 369 329 292 $ 191
IBNR Reserves Dec. 31, 2019 (Audited) $ 1                  
Cumulative Number of Reported Claims (Audited) | item 54,938                  
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 2019) $ 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 2019) 819 799 762 725 660 539 355 187 47  
IBNR Reserves Dec. 31, 2019 (Audited) $ 69                  
Cumulative Number of Reported Claims (Audited) | item 27,557                  
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 2019) $ 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 2019) 2,234 2,222 2,193 2,156 2,088 1,979 1,803 1,573 1,060  
IBNR Reserves Dec. 31, 2019 (Audited) $ 25                  
Cumulative Number of Reported Claims (Audited) | item 125,867                  
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 2019) $ 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 2019) 1,732 1,696 1,652 1,583 1,487 1,365 1,185 911 420  
IBNR Reserves Dec. 31, 2019 (Audited) $ 319                  
Cumulative Number of Reported Claims (Audited) | item 136,801                  
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 2019) $ 506 508 520 545 601 632 639 596 565  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 496 490 476 447 414 324 249 143 33  
IBNR Reserves Dec. 31, 2019 (Audited) $ 2                  
Cumulative Number of Reported Claims (Audited) | item 5,213                  
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 2019) $ 408 417 422 427 434 441 446 438 459  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 401 397 389 371 349 314 280 249 $ 176  
IBNR Reserves Dec. 31, 2019 (Audited) $ (5)                  
Cumulative Number of Reported Claims (Audited) | item 55,773                  
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 2019) $ 920 917 905 892 913 935 985 989    
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 811 754 699 589 489 295 150 32    
IBNR Reserves Dec. 31, 2019 (Audited) $ 78                  
Cumulative Number of Reported Claims (Audited) | item 24,920                  
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 2019) $ 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 2019) 1,804 1,780 1,752 1,699 1,590 1,424 1,246 795    
IBNR Reserves Dec. 31, 2019 (Audited) $ 34                  
Cumulative Number of Reported Claims (Audited) | item 104,921                  
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 2019) $ 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 2019) 1,735 1,689 1,629 1,536 1,394 1,217 940 443    
IBNR Reserves Dec. 31, 2019 (Audited) $ 367                  
Cumulative Number of Reported Claims (Audited) | item 138,034                  
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 2019) $ 593 605 599 601 605 614 591 538    
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 453 436 419 383 342 255 160 38    
IBNR Reserves Dec. 31, 2019 (Audited) $ 60                  
Cumulative Number of Reported Claims (Audited) | item 4,865                  
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 2019) $ 362 374 380 397 398 414 413 435    
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 347 342 333 316 288 262 231 $ 165    
IBNR Reserves Dec. 31, 2019 (Audited) $ (2)                  
Cumulative Number of Reported Claims (Audited) | item 51,208                  
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 2019) $ 975 933 927 940 958 975 965      
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 816 745 639 498 363 175 35      
IBNR Reserves Dec. 31, 2019 (Audited) $ 104                  
Cumulative Number of Reported Claims (Audited) | item 22,625                  
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 2019) $ 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 2019) 1,516 1,475 1,410 1,304 1,167 987 644      
IBNR Reserves Dec. 31, 2019 (Audited) $ 38                  
Cumulative Number of Reported Claims (Audited) | item 83,818                  
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 2019) $ 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 2019) 1,659 1,604 1,525 1,413 1,237 954 458      
IBNR Reserves Dec. 31, 2019 (Audited) $ 408                  
Cumulative Number of Reported Claims (Audited) | item 134,091                  
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 2019) $ 586 607 654 630 606 565 510      
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 451 434 400 352 252 154 34      
IBNR Reserves Dec. 31, 2019 (Audited) $ 42                  
Cumulative Number of Reported Claims (Audited) | item 4,456                  
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 2019) $ 433 443 444 457 469 478 485      
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 405 387 369 336 304 272 $ 194      
IBNR Reserves Dec. 31, 2019 (Audited) $ 0                  
Cumulative Number of Reported Claims (Audited) | item 54,251                  
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 2019) $ 1,013 956 948 983 989 976        
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 750 640 515 321 163 37        
IBNR Reserves Dec. 31, 2019 (Audited) $ 159                  
Cumulative Number of Reported Claims (Audited) | item 22,319                  
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 2019) $ 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 2019) 1,512 1,448 1,328 1,154 956 628        
IBNR Reserves Dec. 31, 2019 (Audited) $ 50                  
Cumulative Number of Reported Claims (Audited) | item 78,292                  
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 2019) $ 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 2019) 1,581 1,505 1,399 1,224 944 455        
IBNR Reserves Dec. 31, 2019 (Audited) $ 486                  
Cumulative Number of Reported Claims (Audited) | item 129,293                  
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 2019) $ 452 473 518 563 571 549        
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 407 367 312 239 150 38        
IBNR Reserves Dec. 31, 2019 (Audited) $ 32                  
Cumulative Number of Reported Claims (Audited) | item 4,356                  
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 2019) $ 423 426 433 445 444 429        
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 384 362 331 302 265 $ 189        
IBNR Reserves Dec. 31, 2019 (Audited) $ (9)                  
Cumulative Number of Reported Claims (Audited) | item 52,268                  
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 2019) $ 1,057 967 923 956 998          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 740 558 336 137 36          
IBNR Reserves Dec. 31, 2019 (Audited) $ 165                  
Cumulative Number of Reported Claims (Audited) | item 21,360                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Business Insurance [Member] | Commercial property [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) $ 737 731 741 750 786          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 717 699 681 615 376          
IBNR Reserves Dec. 31, 2019 (Audited) $ 8                  
Cumulative Number of Reported Claims (Audited) | item 20,162                  
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 2019) $ 1,606 1,597 1,593 1,625 1,568          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,409 1,310 1,144 970 595          
IBNR Reserves Dec. 31, 2019 (Audited) $ 92                  
Cumulative Number of Reported Claims (Audited) | item 71,635                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Business Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) $ 1,298 1,283 1,234 1,202 1,188          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,181 1,058 885 650 405          
IBNR Reserves Dec. 31, 2019 (Audited) $ 48                  
Cumulative Number of Reported Claims (Audited) | item 173,545                  
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 2019) $ 2,372 2,441 2,505 2,585 2,644          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,411 1,310 1,154 893 430          
IBNR Reserves Dec. 31, 2019 (Audited) $ 636                  
Cumulative Number of Reported Claims (Audited) | item 123,163                  
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 2019) $ 395 437 486 524 528          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 338 310 234 141 38          
IBNR Reserves Dec. 31, 2019 (Audited) $ 38                  
Cumulative Number of Reported Claims (Audited) | item 4,195                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Bond & Specialty Insurance [Member] | Fidelity and surety [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) $ 137 145 179 191 217          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 88 86 87 75 32          
IBNR Reserves Dec. 31, 2019 (Audited) $ 32                  
Cumulative Number of Reported Claims (Audited) | item 834                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Personal Insurance [Member] | Automobile [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) $ 2,219 2,222 2,236 2,244 2,186          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 2,174 2,109 1,985 1,768 1,319          
IBNR Reserves Dec. 31, 2019 (Audited) $ 11                  
Cumulative Number of Reported Claims (Audited) | item 757,972                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Personal Insurance [Member] | Homeowners (excluding Other) [Member]                    
Claims Development                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) $ 1,443 1,452 1,461 1,454 1,438          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,429 1,421 1,395 1,333 994          
IBNR Reserves Dec. 31, 2019 (Audited) $ 1                  
Cumulative Number of Reported Claims (Audited) | item 145,136                  
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 2019) $ 358 356 360 360 361          
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 307 282 253 226 $ 162          
IBNR Reserves Dec. 31, 2019 (Audited) $ 10                  
Cumulative Number of Reported Claims (Audited) | item 45,203                  
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 2019) $ 1,187 1,087 1,058 1,075            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 649 421 191 35            
IBNR Reserves Dec. 31, 2019 (Audited) $ 359                  
Cumulative Number of Reported Claims (Audited) | item 19,997                  
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 2019) $ 809 820 863 896            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 767 745 685 441            
IBNR Reserves Dec. 31, 2019 (Audited) $ 11                  
Cumulative Number of Reported Claims (Audited) | item 22,313                  
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 2019) $ 1,590 1,598 1,623 1,662            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,278 1,133 950 585            
IBNR Reserves Dec. 31, 2019 (Audited) $ 122                  
Cumulative Number of Reported Claims (Audited) | item 68,888                  
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 2019) $ 1,409 1,371 1,303 1,278            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,158 931 688 412            
IBNR Reserves Dec. 31, 2019 (Audited) $ 94                  
Cumulative Number of Reported Claims (Audited) | item 183,114                  
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 2019) $ 2,473 2,569 2,690 2,768            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,272 1,118 873 421            
IBNR Reserves Dec. 31, 2019 (Audited) $ 702                  
Cumulative Number of Reported Claims (Audited) | item 122,944                  
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 2019) $ 520 504 511 512            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 313 233 141 30            
IBNR Reserves Dec. 31, 2019 (Audited) $ 91                  
Cumulative Number of Reported Claims (Audited) | item 4,326                  
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 2019) $ 208 205 239 226            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 149 142 121 54            
IBNR Reserves Dec. 31, 2019 (Audited) $ 9                  
Cumulative Number of Reported Claims (Audited) | item 886                  
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 2019) $ 2,752 2,772 2,791 2,779            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 2,616 2,466 2,203 1,610            
IBNR Reserves Dec. 31, 2019 (Audited) $ 44                  
Cumulative Number of Reported Claims (Audited) | item 922,014                  
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 2019) $ 1,511 1,525 1,547 1,556            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,479 1,455 1,392 1,049            
IBNR Reserves Dec. 31, 2019 (Audited) $ 8                  
Cumulative Number of Reported Claims (Audited) | item 143,949                  
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 2019) $ 419 409 409 361            
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 343 310 283 $ 211            
IBNR Reserves Dec. 31, 2019 (Audited) $ 19                  
Cumulative Number of Reported Claims (Audited) | item 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 2019) $ 1,196 1,143 1,133              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 378 180 40              
IBNR Reserves Dec. 31, 2019 (Audited) $ 530                  
Cumulative Number of Reported Claims (Audited) | item 18,014                  
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 2019) $ 1,151 1,177 1,209              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,073 1,003 618              
IBNR Reserves Dec. 31, 2019 (Audited) $ 11                  
Cumulative Number of Reported Claims (Audited) | item 25,066                  
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 2019) $ 1,956 1,928 1,872              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,388 1,199 716              
IBNR Reserves Dec. 31, 2019 (Audited) $ 266                  
Cumulative Number of Reported Claims (Audited) | item 71,220                  
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 2019) $ 1,524 1,501 1,386              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,027 746 456              
IBNR Reserves Dec. 31, 2019 (Audited) $ 219                  
Cumulative Number of Reported Claims (Audited) | item 191,166                  
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 2019) $ 2,584 2,681 2,779              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,154 890 433              
IBNR Reserves Dec. 31, 2019 (Audited) $ 918                  
Cumulative Number of Reported Claims (Audited) | item 120,900                  
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 2019) $ 526 517 534              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 262 155 38              
IBNR Reserves Dec. 31, 2019 (Audited) $ 174                  
Cumulative Number of Reported Claims (Audited) | item 4,455                  
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 2019) $ 240 271 244              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 194 166 70              
IBNR Reserves Dec. 31, 2019 (Audited) $ 22                  
Cumulative Number of Reported Claims (Audited) | item 905                  
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 2019) $ 3,221 3,256 3,323              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 2,887 2,575 1,912              
IBNR Reserves Dec. 31, 2019 (Audited) $ 139                  
Cumulative Number of Reported Claims (Audited) | item 1,061,907                  
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 2019) $ 2,343 2,340 2,312              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 2,197 2,059 1,471              
IBNR Reserves Dec. 31, 2019 (Audited) $ 49                  
Cumulative Number of Reported Claims (Audited) | item 169,085                  
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 2019) $ 403 381 346              
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 296 257 $ 182              
IBNR Reserves Dec. 31, 2019 (Audited) $ 34                  
Cumulative Number of Reported Claims (Audited) | item 46,769                  
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 2019) $ 1,312 1,253                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 202 42                
IBNR Reserves Dec. 31, 2019 (Audited) $ 841                  
Cumulative Number of Reported Claims (Audited) | item 16,694                  
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 2019) $ 1,079 1,093                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 928 561                
IBNR Reserves Dec. 31, 2019 (Audited) $ 10                  
Cumulative Number of Reported Claims (Audited) | item 24,785                  
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 2019) $ 2,114 1,976                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,302 792                
IBNR Reserves Dec. 31, 2019 (Audited) $ 416                  
Cumulative Number of Reported Claims (Audited) | item 68,403                  
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 2019) $ 1,742 1,645                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 848 515                
IBNR Reserves Dec. 31, 2019 (Audited) $ 469                  
Cumulative Number of Reported Claims (Audited) | item 201,578                  
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 2019) $ 2,687 2,744                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 919 440                
IBNR Reserves Dec. 31, 2019 (Audited) $ 1,180                  
Cumulative Number of Reported Claims (Audited) | item 121,460                  
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 2019) $ 548 530                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 182 49                
IBNR Reserves Dec. 31, 2019 (Audited) $ 243                  
Cumulative Number of Reported Claims (Audited) | item 4,393                  
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 2019) $ 235 220                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 171 64                
IBNR Reserves Dec. 31, 2019 (Audited) $ 22                  
Cumulative Number of Reported Claims (Audited) | item 849                  
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 2019) $ 3,269 3,281                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 2,582 1,889                
IBNR Reserves Dec. 31, 2019 (Audited) $ 347                  
Cumulative Number of Reported Claims (Audited) | item 1,048,084                  
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 2019) $ 2,574 2,610                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 2,298 1,657                
IBNR Reserves Dec. 31, 2019 (Audited) $ 112                  
Cumulative Number of Reported Claims (Audited) | item 185,384                  
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 2019) $ 462 440                
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 305 $ 219                
IBNR Reserves Dec. 31, 2019 (Audited) $ 64                  
Cumulative Number of Reported Claims (Audited) | item 50,302                  
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 2019) $ 1,447                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 51                  
IBNR Reserves Dec. 31, 2019 (Audited) $ 1,231                  
Cumulative Number of Reported Claims (Audited) | item 12,167                  
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 2019) $ 1,069                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 610                  
IBNR Reserves Dec. 31, 2019 (Audited) $ 84                  
Cumulative Number of Reported Claims (Audited) | item 22,186                  
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 2019) $ 2,017                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 707                  
IBNR Reserves Dec. 31, 2019 (Audited) $ 715                  
Cumulative Number of Reported Claims (Audited) | item 70,798                  
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 2019) $ 1,835                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 539                  
IBNR Reserves Dec. 31, 2019 (Audited) $ 838                  
Cumulative Number of Reported Claims (Audited) | item 167,863                  
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 2019) $ 2,680                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 466                  
IBNR Reserves Dec. 31, 2019 (Audited) $ 1,619                  
Cumulative Number of Reported Claims (Audited) | item 107,298                  
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 2019) $ 588                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 51                  
IBNR Reserves Dec. 31, 2019 (Audited) $ 432                  
Cumulative Number of Reported Claims (Audited) | item 3,400                  
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 2019) $ 203                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 49                  
IBNR Reserves Dec. 31, 2019 (Audited) $ 116                  
Cumulative Number of Reported Claims (Audited) | item 592                  
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 2019) $ 3,362                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,933                  
IBNR Reserves Dec. 31, 2019 (Audited) $ 858                  
Cumulative Number of Reported Claims (Audited) | item 940,933                  
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 2019) $ 2,297                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 1,613                  
IBNR Reserves Dec. 31, 2019 (Audited) $ 447                  
Cumulative Number of Reported Claims (Audited) | item 158,328                  
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 2019) $ 445                  
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Audited for 2019) 216                  
IBNR Reserves Dec. 31, 2019 (Audited) $ 110                  
Cumulative Number of Reported Claims (Audited) | item 44,796