Medical Claims Payable (Narrative) (Details) $ in Millions	Jun. 30, 2019 USD ($)
Short-duration Insurance Contracts, Claim Year 2019 [Member] | Commercial Specialty Business Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2,533
Short-duration Insurance Contracts, Claim Year 2019 [Member] | Government Business Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	5,337
Short-duration Insurance Contracts, Claim Year 2018 [Member] | Commercial Specialty Business Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	267
Short-duration Insurance Contracts, Claim Year 2018 [Member] | Government Business Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	289
Short-duration Insurance Contracts, Claim Year 2017 and Prior [Member] | Commercial Specialty Business Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	45
Short-duration Insurance Contracts, Claim Year 2017 and Prior [Member] | Government Business Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 35