Quarterly report pursuant to Section 13 or 15(d)

Medical Claims Liability (Narrative) (Details)

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Medical Claims Liability (Narrative) (Details) - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Insurance [Abstract]    
Amounts recorded as an adjustment to premium revenues related to minimum HBR and return of premium programs $ (4) $ 27
Short-duration insurance contracts, Incurred but not reported and expected development on reported claims $ 3,292