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Other Commitments And Contingencies (Estimated Incident Expenses) (Details) - USD ($) $ in Millions | 12 Months Ended | 16 Months Ended | 28 Months Ended
--- | --- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2020
Estimated Incident Expenses [Line Items] |  |  |
Expenses Related to Third-Party Claims, Fines, Penalties, and settlements | $ (5) | $ 1,041 | $ 1,036
Expenses Other Than Third Party Claims | $ 22 | $ 420 | 442
Maximum | Columbia Of Massachusetts |  |  |
Estimated Incident Expenses [Line Items] |  |  |
Expenses Related to Third-Party Claims, Fines, Penalties, and settlements |  |  | 1,050
Expenses Other Than Third Party Claims |  |  | 450
Minimum | Columbia Of Massachusetts |  |  |
Estimated Incident Expenses [Line Items] |  |  |
Expenses Related to Third-Party Claims, Fines, Penalties, and settlements |  |  | 1,036
Expenses Other Than Third Party Claims |  |  | $ 445

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