Segment Information (Major Product Revenues) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	$ 103,141	$ 91,341	$ 89,061
Commercial and Specialty Business Segment [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	37,421	35,782	40,363
Commercial and Specialty Business Segment [Member] | Managed Care Products [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	30,311	29,012	33,971
Commercial and Specialty Business Segment [Member] | Managed Care Services [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	5,451	5,218	4,732
Commercial and Specialty Business Segment [Member] | Dental Vision Products And Services [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	1,302	1,220	1,218
Commercial and Specialty Business Segment [Member] | Other Products [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	357	332	442
Government Business Segment [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	62,632	55,348	48,587
Government Business Segment [Member] | Managed Care Products [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	62,229	54,889	48,144
Government Business Segment [Member] | Managed Care Services [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	403	459	443
Other Segment [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	7,695	1,519	127
Segment Eliminations [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	$ (4,607)	$ (1,308)	$ (16)