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Reinsurance (Components of Written Premiums) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Premiums Written, Net [Abstract] |  |  |
Direct | $ 14,264 | $ 13,587 | $ 12,612
Assumed | 281 | 303 | 279
Ceded | 5,417 | 5,485 | 4,832
Net | 9,128 | 8,405 | 8,059
Property and casualty |  |  |
Premiums Written, Net [Abstract] |  |  |
Direct | 13,843 | 13,150 | 12,168
Assumed | 235 | 255 | 229
Ceded | 5,417 | 5,485 | 4,832
Net | 8,661 | 7,920 | 7,565
Long term care |  |  |
Premiums Written, Net [Abstract] |  |  |
Direct | 421 | 437 | 444
Assumed | 46 | 48 | 50
Ceded | 0 | 0 | 0
Net | $ 467 | $ 485 | $ 494
Percentage of assumed premiums written to net premiums written |  |  |
Premiums Written, Net [Abstract] |  |  |
Assumed/ Net % | 3.10% | 3.60% | 3.50%
Percentage of assumed premiums written to net premiums written | Property and casualty |  |  |
Premiums Written, Net [Abstract] |  |  |
Assumed/ Net % | 2.70% | 3.20% | 3.00%
Percentage of assumed premiums written to net premiums written | Long term care |  |  |
Premiums Written, Net [Abstract] |  |  |
Assumed/ Net % | 9.90% | 9.90% | 10.10%

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- Definition Amount, before premiums ceded to other entities and premiums assumed by the entity, of premiums written. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI https://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 + Details
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