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Reinsurance (Components of Written Premiums) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Premiums Written, Net [Abstract] |  |  |
Direct | $ 13,587 | $ 12,612 | $ 11,894
Assumed | 303 | 279 | 331
Ceded | 5,485 | 4,832 | 4,569
Net | 8,405 | 8,059 | 7,656
Property and casualty |  |  |
Premiums Written, Net [Abstract] |  |  |
Direct | 13,150 | 12,168 | 11,421
Assumed | 255 | 229 | 281
Ceded | 5,485 | 4,832 | 4,569
Net | 7,920 | 7,565 | 7,133
Long term care |  |  |
Premiums Written, Net [Abstract] |  |  |
Direct | 437 | 444 | 473
Assumed | 48 | 50 | 50
Ceded | 0 | 0 | 0
Net | $ 485 | $ 494 | $ 523
Percentage of assumed premiums written to net premiums written |  |  |
Premiums Written, Net [Abstract] |  |  |
Assumed/ Net % | 3.60% | 3.50% | 4.30%
Percentage of assumed premiums written to net premiums written | Property and casualty |  |  |
Premiums Written, Net [Abstract] |  |  |
Assumed/ Net % | 3.20% | 3.00% | 3.90%
Percentage of assumed premiums written to net premiums written | Long term care |  |  |
Premiums Written, Net [Abstract] |  |  |
Assumed/ Net % | 9.90% | 10.10% | 9.60%

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- Definition Amount of written premiums assumed from other entities. + 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)(2) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 + Details
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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 http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 + Details
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