Medical Claims Payable (Narrative) (Details) $ in Millions	Jun. 30, 2021 USD ($)
Short-Duration Insurance Contract, Accident Year 2019 [Member] | Commercial Specialty Business Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 71
Short-Duration Insurance Contract, Accident Year 2019 [Member] | Government Business Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	105
Short-Duration Insurance Contract, Accident Year 2019 [Member] | Other Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	0
Short-Duration Insurance Contract, Accident Year 2020 [Member] | Commercial Specialty Business Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	486
Short-Duration Insurance Contract, Accident Year 2020 [Member] | Government Business Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	862
Short-Duration Insurance Contract, Accident Year 2020 [Member] | Other Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	25
Short-Duration Insurance Contract, Accident Year 2021 [Member] | Commercial Specialty Business Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	3,065
Short-Duration Insurance Contract, Accident Year 2021 [Member] | Government Business Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	7,961
Short-Duration Insurance Contract, Accident Year 2021 [Member] | Other Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 205