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Reserve for Property-Liability Insurance Claims and Claims Expense - Incurred and claims expense narrative (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Increase (decrease) in claims and claims expense |  |  |
Losses from catastrophes, net of recoveries | $ 22,778 | $ 21,847 | $ 22,160
Net increase (decrease) to reserves | 255 | 503 | 17
Auto |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | (455) | 490 | 155
Commercial lines |  |  |
Increase (decrease) in claims and claims expense |  |  |
Losses from catastrophes, net of recoveries | 545 |  |
Net increase (decrease) to reserves | (108) |  |
Homeowners |  |  |
Increase (decrease) in claims and claims expense |  |  |
Losses from catastrophes, net of recoveries | 4,817 |  |
Other personal lines |  |  |
Increase (decrease) in claims and claims expense |  |  |
Losses from catastrophes, net of recoveries | 1,081 |  |
Catastrophes |  |  |
Increase (decrease) in claims and claims expense |  |  |
Losses from catastrophes, net of recoveries | 2,860 | 3,230 | 2,570
Catastrophe loss reestimates |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | (25) | 18 | (6)
Catastrophe loss reestimates | Homeowners |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves |  |  | 24
Reserve reestimates | Homeowners |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | (14) | 131 |
Reserve reestimates | Other personal lines |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | 9 | (22) | (57)
Reserve reestimates | Discontinued Lines and Coverages |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | (87) | $ (96) | $ (105)
Discontinued Lines and Coverages |  |  |
Increase (decrease) in claims and claims expense |  |  |
Losses from catastrophes, net of recoveries | $ 73 |  |

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- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred and costs incurred in the claim settlement process. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 + Details
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- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 + Details
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