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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, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Increase (decrease) in claims and claims expense |  |  |
Losses from catastrophes, net of recoveries | $ 23,976 | $ 22,778 | $ 21,847
Net increase (decrease) to reserves | 130 | 255 | 503
Auto |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | 323 | 455 | 490
Homeowners |  |  |
Increase (decrease) in claims and claims expense |  |  |
Losses from catastrophes, net of recoveries | 4,625 |  |
Other personal lines |  |  |
Increase (decrease) in claims and claims expense |  |  |
Losses from catastrophes, net of recoveries | 1,024 |  |
Net increase (decrease) to reserves | (8) | 7 | (1)
Commercial lines |  |  |
Increase (decrease) in claims and claims expense |  |  |
Losses from catastrophes, net of recoveries | 648 |  |
Net increase (decrease) to reserves | (17) | (108) | (19)
Discontinued Lines and Coverages |  |  |
Increase (decrease) in claims and claims expense |  |  |
Unfavorable reestimate | 95 |  |
Commercial Lines, Discontinued Lines and Coverages and Other Personal Lines [Member] |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | 2 | 2 | (2)
Catastrophes |  |  |
Increase (decrease) in claims and claims expense |  |  |
Losses from catastrophes, net of recoveries | 2,560 | 2,860 | 3,230
Catastrophes | Auto |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | 17 | 39 | 15
Catastrophes | Homeowners |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | (66) | (65) | 7
Catastrophes | Other personal lines |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | 0 | 1 | (3)
Catastrophes | Commercial lines |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | 1 | 0 | (1)
Catastrophes | Discontinued Lines and Coverages |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | 0 | 0 | 0
Catastrophes | Commercial Lines, Discontinued Lines and Coverages and Other Personal Lines [Member] |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | 0 | 0 | 0
Catastrophe loss reestimates |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | (48) | (25) | 18
Reserve reestimates | Homeowners |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | (65) | (14) | 131
Reserve reestimates | Discontinued Lines and Coverages |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | (105) | (87) | (96)
Discontinued Lines and Coverages |  |  |
Increase (decrease) in claims and claims expense |  |  |
Losses from catastrophes, net of recoveries | 91 |  |
Non-catastrophe losses |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | 178 | 280 | 485
Non-catastrophe losses | Auto |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | 306 | 416 | 475
Non-catastrophe losses | Homeowners |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | 1 | 51 | 124
Non-catastrophe losses | Other personal lines |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | (8) | 6 | 2
Non-catastrophe losses | Commercial lines |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | (18) | (108) | (18)
Non-catastrophe losses | Discontinued Lines and Coverages |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | (105) | (87) | (96)
Non-catastrophe losses | Commercial Lines, Discontinued Lines and Coverages and Other Personal Lines [Member] |  |  |
Increase (decrease) in claims and claims expense |  |  |
Net increase (decrease) to reserves | $ 2 | $ 2 | $ (2)

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