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Quarterly Operating Results (Unaudited) - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Quarterly Operating Results (Unaudited) [Line Items] |  |  |  |  |  |
Increase (decrease) in holding company expenses related to employee benefit plans | $ 20 |  |  |  |  |
Property and casualty insurance | Other lines |  |  |  |  |  |
Quarterly Operating Results (Unaudited) [Line Items] |  |  |  |  |  |
Increase in asbestos and environmental reserves |  | $ 18 | $ 18 | $ 18 | $ 18 | $ 89
Special charges related to the exit of certain lines of business within subsidiaries | 76 |  |  |  |  |
Other |  |  |  |  |  |
Quarterly Operating Results (Unaudited) [Line Items] |  |  |  |  |  |
Write off of deferred debt issuance cost due to the retirement of debt | $ 5 |  |  |  |  |
Other | Former railroad and manufacturing operations |  |  |  |  |  |
Quarterly Operating Results (Unaudited) [Line Items] |  |  |  |  |  |
Increase in asbestos and environmental reserves |  | $ 11 | $ 9 |  |  |

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- Definition Amount, after effects of reinsurance, of expense for claims incurred and costs incurred in the claim settlement process attributable to asbestos and environmental claims. + 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=116884095&loc=d3e14764-158437 + Details
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