Medical Claims Payable (Reconciliation of Net Incurred Medical Claims to Benefit Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Net Incurred Medical Claims to Benefit Expense [Line Items]
Net incurred medical claims	$ 84,457	$ 78,195	$ 68,651
Quality improvement and other claims expense	3,588	3,591	3,244
Benefit expense	88,045	81,786	71,895
Commercial and Specialty Business Segment [Member]
Reconciliation of Net Incurred Medical Claims to Benefit Expense [Line Items]
Net incurred medical claims	24,519	25,752	23,638
Government Business Segment [Member]
Reconciliation of Net Incurred Medical Claims to Benefit Expense [Line Items]
Net incurred medical claims	58,650	52,443	45,013
Other Segment [Member]
Reconciliation of Net Incurred Medical Claims to Benefit Expense [Line Items]
Net incurred medical claims	$ 1,288	$ 0	$ 0