Medical Claims Payable (Reconciliation of Net Incurred Medical Claims to Benefit Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Net Incurred Medical Claims to Benefit Expense [Line Items]
Net incurred medical claims	$ 68,651	$ 69,244	$ 64,033
Quality Improvement And Other Claims Expense	3,244	2,992	2,801
Benefit expense	71,895	72,236	66,834
Commercial and Specialty Business Segment [Member]
Reconciliation of Net Incurred Medical Claims to Benefit Expense [Line Items]
Net incurred medical claims	23,638	29,005	27,125
Government Business Segment [Member]
Reconciliation of Net Incurred Medical Claims to Benefit Expense [Line Items]
Net incurred medical claims	$ 45,013	$ 40,239	$ 36,908