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Supplementary Insurance Information - Table (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] |  |  |
Deferred policy acquisition costs | $ 267 | $ 244 | $ 322
Reserves for claims and unpaid losses and LAE | 11,074 | 10,392 | 10,232
Unearned premiums | 3,041 | 2,803 | 2,830
Net earned premiums | 5,404 | 5,099 | 5,185
Net investment income | 730 | 461 | 532
Claims, losses and settlement expenses | 3,157 | 3,271 | 3,271
Amortization of deferred policy acquisition costs | 580 | 615 | 721
Other operating expenses | 1,480 | 1,544 | 1,587
Net written premiums | 5,573 | 5,013 | 5,342
Property and casualty insurance |  |  |
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] |  |  |
Deferred policy acquisition costs | 267 | 244 | 322
Reserves for claims and unpaid losses and LAE | 11,074 | 10,392 | 10,232
Unearned premiums | 3,041 | 2,803 | 2,830
Net earned premiums | 5,404 | 5,099 | 5,185
Net investment income | 663 | 399 | 472
Claims, losses and settlement expenses | 3,157 | 3,271 | 3,271
Amortization of deferred policy acquisition costs | 580 | 615 | 721
Other operating expenses | 967 | 1,036 | 1,027
Net written premiums | 5,573 | 5,013 | 5,342
Other |  |  |
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] |  |  |
Net investment income | 67 | 62 | 60
Other operating expenses | $ 513 | $ 508 | $ 560

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