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Litigation and Contingencies (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2018 | Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract] |  |
Average paid claim reduction due to curtailments (as a percent) | 6.30% | 5.60%
Maximum exposure associated with other discussions and legal proceedings | $ 286 |

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- Definition Estimated maximum exposure associated with other discussions and legal proceedings related to claims paying practices. + References No definition available. + Details
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