Annual report pursuant to Section 13 and 15(d)

Medical Claims Liability - Narrative (Details)

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Medical Claims Liability - Narrative (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Insurance [Abstract]      
Amounts recorded as an adjustment to premium revenues related to minimum HBR and return of premium programs $ 49 $ 25 $ 1