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Unpaid losses and loss expenses Unpaid Losses and loss expenses, claims development (Cumulative Net incurred Loss and Allocated Loss Adjustment Expense) (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net $ 64,201                  
North America Commercial P&C Insurance - Workers' Compensation [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 12,683                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 5,456                  
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 10,195                  
Short-Duration PPD (373)                  
North America Commercial P&C Insurance - Liability [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 41,853                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 21,459                  
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 22,401                  
Short-Duration PPD 415                  
North America Commercial P&C Insurance - Other Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 6,902                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 4,348                  
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 2,764                  
Short-Duration PPD 99                  
North America Commercial P&C Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 24,417                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 20,850                  
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 3,572                  
Short-Duration PPD (434)                  
North America Personal P&C Insurance [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 29,329                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 25,183                  
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 4,182                  
Short-Duration PPD (301)                  
Overseas General Insurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 14,949                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 6,954                  
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 8,639                  
Short-Duration PPD (27)                  
Overseas General Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 22,115                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 18,337                  
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 3,907                  
Short-Duration PPD (261)                  
Global Reinsurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 2,708                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 1,647                  
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 1,328                  
Short-Duration PPD 1                  
Global Reinsurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 2,665                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 2,139                  
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 540                  
Short-Duration PPD (28)                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 1,032 $ 1,057 $ 1,092 $ 1,128 $ 1,154 $ 1,217 $ 1,279 $ 1,276 $ 1,259 $ 1,282
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 257                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 679 665 645 628 606 564 501 418 301 116
Cumulative Number of Reported Claims 50,000                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Commercial P&C Insurance - Liability [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 3,587 3,606 3,562 3,694 3,720 3,926 3,959 3,803 3,694 3,546
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 293                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 3,171 3,074 2,916 2,739 2,523 2,283 1,849 1,201 603 138
Cumulative Number of Reported Claims 27,000                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 450 455 456 461 453 456 513 499 468 485
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 12                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 432 430 422 410 393 369 303 214 137 47
Cumulative Number of Reported Claims 15,000                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,587 1,586 1,588 1,584 1,581 1,596 1,629 1,641 1,735 1,726
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net (1)                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,583 1,579 1,579 1,579 1,566 1,564 1,548 1,480 1,336 723
Cumulative Number of Reported Claims 545,000                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | North America Personal P&C Insurance [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,561 2,552 2,555 2,553 2,556 2,550 2,530 2,547 2,536 2,482
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 19                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,533 2,537 2,530 2,520 2,495 2,466 2,380 2,259 2,073 1,491
Cumulative Number of Reported Claims 148,000                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Overseas General Insurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,147 1,158 1,158 1,143 1,159 1,213 1,231 1,209 1,182 1,092
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 67                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 985 946 915 884 812 736 622 453 259 76
Cumulative Number of Reported Claims 40,000                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Overseas General Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,787 1,780 1,785 1,785 1,803 1,809 1,825 1,854 1,877 1,763
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 11                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,757 1,752 1,753 1,750 1,733 1,706 1,685 1,610 1,394 764
Cumulative Number of Reported Claims 556,000                  
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Global Reinsurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 309 308 308 305 301 305 297 296 286 281
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 8                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 288 281 273 264 248 231 216 190 158 89
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Global Reinsurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 153 154 154 154 156 151 158 158 152 144
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 0                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 150 150 150 149 148 144 140 130 102 $ 56
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 1,117 1,162 1,177 1,206 1,269 1,378 1,383 1,361 1,366  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 299                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 707 683 653 621 584 529 452 326 122  
Cumulative Number of Reported Claims 51,000                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Commercial P&C Insurance - Liability [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 3,693 3,655 3,751 3,759 3,787 3,790 3,678 3,582 3,520  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 324                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 3,105 2,979 2,818 2,591 2,330 1,972 1,333 661 171  
Cumulative Number of Reported Claims 27,000                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 466 473 469 479 480 523 526 500 503  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 13                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 441 437 424 398 374 323 246 145 52  
Cumulative Number of Reported Claims 16,000                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,808 1,815 1,813 1,817 1,805 1,769 1,789 1,879 1,899  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 13                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,791 1,784 1,783 1,772 1,748 1,721 1,646 1,495 842  
Cumulative Number of Reported Claims 650,000                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | North America Personal P&C Insurance [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,468 2,462 2,460 2,452 2,459 2,471 2,533 2,523 2,428  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 16                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,439 2,435 2,417 2,386 2,359 2,303 2,201 2,042 1,446  
Cumulative Number of Reported Claims 154,000                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Overseas General Insurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,265 1,253 1,240 1,306 1,298 1,308 1,282 1,220 1,127  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 126                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,006 979 956 837 747 632 492 299 117  
Cumulative Number of Reported Claims 42,000                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Overseas General Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,825 1,844 1,857 1,859 1,828 1,824 1,845 1,859 1,867  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 10                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,799 1,794 1,790 1,785 1,776 1,753 1,687 1,506 905  
Cumulative Number of Reported Claims 568,000                  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Global Reinsurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 252 251 244 239 239 230 231 223 219  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 10                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 228 217 207 190 173 157 141 112 57  
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Global Reinsurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 178 178 178 178 181 184 182 179 174  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 1                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 175 174 173 173 169 164 153 127 $ 55  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 1,069 1,121 1,176 1,376 1,393 1,399 1,380 1,412    
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 329                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 648 626 601 564 516 437 313 120    
Cumulative Number of Reported Claims 50,000                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Commercial P&C Insurance - Liability [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 3,517 3,487 3,428 3,539 3,617 3,566 3,485 3,310    
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 446                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,866 2,624 2,320 1,998 1,696 1,158 615 160    
Cumulative Number of Reported Claims 26,000                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 609 602 590 603 615 576 564 530    
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 19                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 560 538 496 445 380 312 175 65    
Cumulative Number of Reported Claims 17,000                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,490 2,500 2,514 2,504 2,513 2,496 2,599 2,695    
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 44                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,445 2,442 2,422 2,399 2,385 2,295 2,080 975    
Cumulative Number of Reported Claims 764,000                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Personal P&C Insurance [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 3,006 3,005 2,995 2,986 2,986 2,990 3,057 3,022    
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 9                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,978 2,966 2,925 2,858 2,788 2,656 2,509 1,690    
Cumulative Number of Reported Claims 163,000                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Overseas General Insurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,268 1,268 1,303 1,268 1,302 1,256 1,210 1,113    
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 109                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,035 974 921 796 638 488 292 88    
Cumulative Number of Reported Claims 43,000                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Overseas General Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,053 2,016 2,049 2,052 2,028 2,045 2,059 2,018    
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 38                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,994 1,994 2,017 1,959 1,920 1,850 1,687 955    
Cumulative Number of Reported Claims 577,000                  
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Global Reinsurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 224 221 214 214 213 216 211 210    
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 7                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 196 186 173 153 138 121 99 46    
Short-duration Insurance Contracts, Accident Year 2017 [Member] | Global Reinsurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 453 454 455 452 448 450 420 394    
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 7                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 441 439 433 426 413 399 321 $ 191    
Short-duration Insurance Contracts, Accident Year 2018 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 1,175 1,221 1,384 1,384 1,379 1,361 1,359      
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 381                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 681 641 597 528 451 329 130      
Cumulative Number of Reported Claims 52,000                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | North America Commercial P&C Insurance - Liability [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 3,987 3,910 3,894 3,813 3,681 3,479 3,362      
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 586                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 3,068 2,779 2,332 1,771 1,299 752 189      
Cumulative Number of Reported Claims 28,000                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 625 605 575 579 573 562 534      
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 13                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 580 532 471 365 270 169 74      
Cumulative Number of Reported Claims 17,000                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,144 2,156 2,165 2,157 2,165 2,229 2,042      
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 0                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,135 2,132 2,108 2,064 2,008 1,817 1,023      
Cumulative Number of Reported Claims 904,000                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | North America Personal P&C Insurance [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 3,115 3,114 3,125 3,104 3,089 3,023 2,995      
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 20                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 3,066 3,031 2,965 2,851 2,693 2,536 1,918      
Cumulative Number of Reported Claims 170,000                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | Overseas General Insurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,289 1,292 1,313 1,357 1,316 1,257 1,208      
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 107                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 966 859 711 595 459 305 103      
Cumulative Number of Reported Claims 44,000                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | Overseas General Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,931 1,952 1,962 1,993 2,018 2,054 1,969      
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 25                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,861 1,854 1,844 1,829 1,766 1,578 905      
Cumulative Number of Reported Claims 613,000                  
Short-duration Insurance Contracts, Accident Year 2018 [Member] | Global Reinsurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 261 256 249 246 249 242 239      
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 12                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 217 195 168 147 124 95 41      
Short-duration Insurance Contracts, Accident Year 2018 [Member] | Global Reinsurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 277 280 286 281 285 283 276      
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 3                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 272 272 269 265 262 247 $ 94      
Short-Duration Insurance Contract, Accident Year 2019 [Member] | North America Commercial P&C Insurance - Workers' Compensation [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 1,297 1,406 1,409 1,400 1,383 1,390        
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 447                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 692 640 575 467 341 143        
Cumulative Number of Reported Claims 48,000                  
Short-Duration Insurance Contract, Accident Year 2019 [Member] | North America Commercial P&C Insurance - Liability [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 4,007 4,051 4,043 3,851 3,613 3,440        
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 824                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,753 2,384 1,885 1,243 667 175        
Cumulative Number of Reported Claims 30,000                  
Short-Duration Insurance Contract, Accident Year 2019 [Member] | North America Commercial P&C Insurance - Other Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 766 755 742 684 635 605        
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 38                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 684 618 464 318 189 70        
Cumulative Number of Reported Claims 17,000                  
Short-Duration Insurance Contract, Accident Year 2019 [Member] | North America Commercial P&C Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,921 1,917 1,940 1,950 2,027 2,042        
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 12                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,894 1,879 1,853 1,796 1,669 1,026        
Cumulative Number of Reported Claims 1,044,000                  
Short-Duration Insurance Contract, Accident Year 2019 [Member] | North America Personal P&C Insurance [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,971 2,951 2,972 2,980 2,979 2,941        
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 47                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,879 2,817 2,712 2,605 2,426 1,660        
Cumulative Number of Reported Claims 157,000                  
Short-Duration Insurance Contract, Accident Year 2019 [Member] | Overseas General Insurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,227 1,308 1,349 1,362 1,342 1,277        
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 148                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 817 710 634 432 308 114        
Cumulative Number of Reported Claims 43,000                  
Short-Duration Insurance Contract, Accident Year 2019 [Member] | Overseas General Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,912 1,934 1,937 1,949 2,008 1,990        
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net (10)                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,872 1,851 1,819 1,756 1,576 953        
Cumulative Number of Reported Claims 632,000                  
Short-Duration Insurance Contract, Accident Year 2019 [Member] | Global Reinsurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 241 234 237 237 242 233        
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 27                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 182 162 138 115 89 39        
Short-Duration Insurance Contract, Accident Year 2019 [Member] | Global Reinsurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 114 114 118 124 126 128        
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net (1)                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 107 103 101 93 79 $ 35        
Short-Duration Insurance Contract, Accident Year 2020 | North America Commercial P&C Insurance - Workers' Compensation [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 1,395 1,408 1,409 1,388 1,367          
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 690                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 520 466 390 282 111          
Cumulative Number of Reported Claims 32,000                  
Short-Duration Insurance Contract, Accident Year 2020 | North America Commercial P&C Insurance - Liability [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 3,839 3,972 3,914 3,821 4,095          
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 1,124                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,269 1,696 1,146 588 151          
Cumulative Number of Reported Claims 24,000                  
Short-Duration Insurance Contract, Accident Year 2020 | North America Commercial P&C Insurance - Other Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 613 637 655 632 639          
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 68                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 480 400 273 156 54          
Cumulative Number of Reported Claims 11,000                  
Short-Duration Insurance Contract, Accident Year 2020 | North America Commercial P&C Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,658 2,680 2,721 2,937 3,133          
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 41                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,575 2,541 2,462 2,256 1,386          
Cumulative Number of Reported Claims 1,126,000                  
Short-Duration Insurance Contract, Accident Year 2020 | North America Personal P&C Insurance [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,577 2,577 2,620 2,622 2,914          
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 59                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,433 2,359 2,218 1,985 1,328          
Cumulative Number of Reported Claims 123,000                  
Short-Duration Insurance Contract, Accident Year 2020 | Overseas General Insurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,278 1,498 1,485 1,565 1,644          
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 415                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 638 516 417 265 99          
Cumulative Number of Reported Claims 35,000                  
Short-Duration Insurance Contract, Accident Year 2020 | Overseas General Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,989 2,017 2,067 2,189 2,319          
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 82                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,810 1,811 1,700 1,560 979          
Cumulative Number of Reported Claims 534,000                  
Short-Duration Insurance Contract, Accident Year 2020 | Global Reinsurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 232 237 237 246 242          
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 30                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 168 148 124 98 41          
Short-Duration Insurance Contract, Accident Year 2020 | Global Reinsurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 278 278 276 252 208          
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 17                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 242 231 214 176 $ 62          
Short-Duration Insurance Contract, Accident Year 2021 | North America Commercial P&C Insurance - Workers' Compensation [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 1,370 1,372 1,330 1,348            
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 618                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 552 458 331 120            
Cumulative Number of Reported Claims 36,000                  
Short-Duration Insurance Contract, Accident Year 2021 | North America Commercial P&C Insurance - Liability [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 4,532 4,434 4,343 4,310            
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 1,984                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,927 1,198 608 173            
Cumulative Number of Reported Claims 25,000                  
Short-Duration Insurance Contract, Accident Year 2021 | North America Commercial P&C Insurance - Other Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 762 746 709 674            
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 188                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 439 293 176 60            
Cumulative Number of Reported Claims 15,000                  
Short-Duration Insurance Contract, Accident Year 2021 | North America Commercial P&C Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,544 2,625 2,820 2,936            
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 53                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,438 2,319 2,098 1,084            
Cumulative Number of Reported Claims 865,000                  
Short-Duration Insurance Contract, Accident Year 2021 | North America Personal P&C Insurance [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,971 2,958 2,871 3,019            
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 147                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,695 2,577 2,364 1,581            
Cumulative Number of Reported Claims 131,000                  
Short-Duration Insurance Contract, Accident Year 2021 | Overseas General Insurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,653 1,649 1,625 1,579            
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 791                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 590 422 262 108            
Cumulative Number of Reported Claims 37,000                  
Short-Duration Insurance Contract, Accident Year 2021 | Overseas General Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,185 2,208 2,321 2,407            
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 2                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,005 1,922 1,654 920            
Cumulative Number of Reported Claims 543,000                  
Short-Duration Insurance Contract, Accident Year 2021 | Global Reinsurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 274 286 281 278            
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 75                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 147 119 87 35            
Short-Duration Insurance Contract, Accident Year 2021 | Global Reinsurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 356 353 350 340            
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 21                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 320 307 277 $ 157            
Short-Duration Insurance Contract, Accident Year 2022 | North America Commercial P&C Insurance - Workers' Compensation [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 1,435 1,407 1,344              
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 769                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 472 332 131              
Cumulative Number of Reported Claims 39,000                  
Short-Duration Insurance Contract, Accident Year 2022 | North America Commercial P&C Insurance - Liability [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 4,656 4,561 4,556              
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 2,689                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,278 648 144              
Cumulative Number of Reported Claims 26,000                  
Short-Duration Insurance Contract, Accident Year 2022 | North America Commercial P&C Insurance - Other Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 846 800 781              
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 243                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 399 234 82              
Cumulative Number of Reported Claims 22,000                  
Short-Duration Insurance Contract, Accident Year 2022 | North America Commercial P&C Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,806 2,941 3,042              
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 155                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,491 2,186 1,048              
Cumulative Number of Reported Claims 904,000                  
Short-Duration Insurance Contract, Accident Year 2022 | North America Personal P&C Insurance [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,938 2,947 3,093              
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 277                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,470 2,271 1,406              
Cumulative Number of Reported Claims 120,000                  
Short-Duration Insurance Contract, Accident Year 2022 | Overseas General Insurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,932 1,761 1,714              
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 1,121                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 510 277 80              
Cumulative Number of Reported Claims 38,000                  
Short-Duration Insurance Contract, Accident Year 2022 | Overseas General Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,535 2,626 2,664              
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 14                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,237 1,960 1,090              
Cumulative Number of Reported Claims 615,000                  
Short-Duration Insurance Contract, Accident Year 2022 | Global Reinsurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 292 296 294              
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 116                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 122 86 39              
Short-Duration Insurance Contract, Accident Year 2022 | Global Reinsurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 290 311 345              
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 27                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 233 194 $ 73              
Short-Duration Insurance Contract, Accident Year 2023 | North America Commercial P&C Insurance - Workers' Compensation [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 1,413 1,371                
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 798                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 358 129                
Cumulative Number of Reported Claims 38,000                  
Short-Duration Insurance Contract, Accident Year 2023 | North America Commercial P&C Insurance - Liability [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 4,900 4,696                
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 3,406                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 827 196                
Cumulative Number of Reported Claims 30,000                  
Short-Duration Insurance Contract, Accident Year 2023 | North America Commercial P&C Insurance - Other Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 882 843                
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 432                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 248 81                
Cumulative Number of Reported Claims 21,000                  
Short-Duration Insurance Contract, Accident Year 2023 | North America Commercial P&C Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,876 3,066                
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 460                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,131 1,217                
Cumulative Number of Reported Claims 965,000                  
Short-Duration Insurance Contract, Accident Year 2023 | North America Personal P&C Insurance [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 3,065 3,396                
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 537                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 2,241 1,484                
Cumulative Number of Reported Claims 114,000                  
Short-Duration Insurance Contract, Accident Year 2023 | Overseas General Insurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 1,888 1,862                
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 1,293                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 276 77                
Cumulative Number of Reported Claims 38,000                  
Short-Duration Insurance Contract, Accident Year 2023 | Overseas General Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,757 2,847                
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 342                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,861 1,039                
Cumulative Number of Reported Claims 615,000                  
Short-Duration Insurance Contract, Accident Year 2023 | Global Reinsurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 286 274                
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 170                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 69 30                
Short-Duration Insurance Contract, Accident Year 2023 | Global Reinsurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 175 180                
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 45                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 92 $ 36                
Accident years prior to 2015 | North America Commercial P&C Insurance - Workers' Compensation [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 2,968                  
Short-Duration PPD (151)                  
Accident years prior to 2015 | North America Commercial P&C Insurance - Liability [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 2,007                  
Short-Duration PPD 69                  
Accident years prior to 2015 | North America Commercial P&C Insurance - Other Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 210                  
Short-Duration PPD (4)                  
Accident years prior to 2015 | North America Commercial P&C Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 5                  
Short-Duration PPD 18                  
Accident years prior to 2015 | North America Personal P&C Insurance [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 36                  
Short-Duration PPD (11)                  
Accident years prior to 2015 | Overseas General Insurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 644                  
Short-Duration PPD 75                  
Accident years prior to 2015 | Overseas General Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 129                  
Short-Duration PPD (11)                  
Accident years prior to 2015 | Global Reinsurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 267                  
Short-Duration PPD (7)                  
Accident years prior to 2015 | Global Reinsurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 14                  
Short-Duration PPD 0                  
Short-Duration Insurance Contract, Accident Year 2024 | North America Commercial P&C Insurance - Workers' Compensation [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 1,380                  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 981                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 147                  
Cumulative Number of Reported Claims 33,000                  
Short-Duration Insurance Contract, Accident Year 2024 | North America Commercial P&C Insurance - Liability [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 5,135                  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 4,617                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 195                  
Cumulative Number of Reported Claims 28,000                  
Short-Duration Insurance Contract, Accident Year 2024 | North America Commercial P&C Insurance - Other Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 883                  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 676                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 85                  
Cumulative Number of Reported Claims 13,000                  
Short-Duration Insurance Contract, Accident Year 2024 | North America Commercial P&C Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 3,583                  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 1,561                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,367                  
Cumulative Number of Reported Claims 853,000                  
Short-Duration Insurance Contract, Accident Year 2024 | North America Personal P&C Insurance [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 3,657                  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 1,826                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,449                  
Cumulative Number of Reported Claims 88,000                  
Short-Duration Insurance Contract, Accident Year 2024 | Overseas General Insurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 2,002                  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 1,650                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 131                  
Cumulative Number of Reported Claims 31,000                  
Short-Duration Insurance Contract, Accident Year 2024 | Overseas General Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 3,141                  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 847                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net $ 1,141                  
Cumulative Number of Reported Claims 607,000                  
Short-Duration Insurance Contract, Accident Year 2024 | Global Reinsurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net $ 337                  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 252                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 30                  
Short-Duration Insurance Contract, Accident Year 2024 | Global Reinsurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net 391                  
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net 193                  
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net 107                  
Accident years 2015 - 2024 | North America Commercial P&C Insurance - Workers' Compensation [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 7,227                  
Short-Duration PPD (222)                  
Accident years 2015 - 2024 | North America Commercial P&C Insurance - Liability [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 20,394                  
Short-Duration PPD 346                  
Accident years 2015 - 2024 | North America Commercial P&C Insurance - Other Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 2,554                  
Short-Duration PPD 103                  
Accident years 2015 - 2024 | North America Commercial P&C Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 3,567                  
Short-Duration PPD (452)                  
Accident years 2015 - 2024 | North America Personal P&C Insurance [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 4,146                  
Short-Duration PPD (290)                  
Accident years 2015 - 2024 | Overseas General Insurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 7,995                  
Short-Duration PPD (102)                  
Accident years 2015 - 2024 | Overseas General Insurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 3,778                  
Short-Duration PPD (250)                  
Accident years 2015 - 2024 | Global Reinsurance - Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 1,061                  
Short-Duration PPD 8                  
Accident years 2015 - 2024 | Global Reinsurance - Non-Casualty [Member]                    
Claims Development [Line Items]                    
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented 526                  
Short-Duration PPD $ (28)