Medical Claims Payable (Incurred and Paid Claims Development, Net of Reinsurance) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Claims Development [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 223,482
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	214,868
Commercial and Specialty Business [Member]
Claims Development [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	81,121
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	78,096
Commercial and Specialty Business [Member] | Short-duration Insurance Contracts, Claim Year 2017 and Prior [Member]
Claims Development [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	31,241	$ 31,275	$ 31,731
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	31,210	31,160	28,426
Commercial and Specialty Business [Member] | Short-duration Insurance Contracts, Claim Year 2018 [Member]
Claims Development [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	23,938	24,094
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	23,860	21,633
Commercial and Specialty Business [Member] | Short-Duration Insurance Contract, Claim Year 2019 [Member]
Claims Development [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	25,942
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	23,026
Government Business Segment [Member]
Claims Development [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	142,361
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	136,772
Government Business Segment [Member] | Short-duration Insurance Contracts, Claim Year 2017 and Prior [Member]
Claims Development [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	44,120	44,232	44,706
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	44,104	44,147	$ 40,302
Government Business Segment [Member] | Short-duration Insurance Contracts, Claim Year 2018 [Member]
Claims Development [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	45,488	45,686
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	45,400	$ 41,115
Government Business Segment [Member] | Short-Duration Insurance Contract, Claim Year 2019 [Member]
Claims Development [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	52,753
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	$ 47,268