Segment Information Segment Information (Major Product Revenues for Each Reportable Segment) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	$ 25,177	$ 22,715	$ 49,565	$ 45,057
Commercial Specialty Business Segment [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	9,417	9,055	18,809	18,006
Government Business Segment [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	15,538	13,619	30,464	26,972
Other Segment [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	794	350	1,342	710
Segment Eliminations [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	(572)	(309)	(1,050)	(631)
Managed Care Products [Member] | Commercial Specialty Business Segment [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	7,646	7,362	15,264	14,641
Managed Care Products [Member] | Government Business Segment [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	15,444	13,510	30,264	26,750
Managed Care Services [Member] | Commercial Specialty Business Segment [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	1,353	1,304	2,719	2,581
Managed Care Services [Member] | Government Business Segment [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	94	109	200	222
Dental Vision Products And Services [Member] | Commercial Specialty Business Segment [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	327	304	650	608
Other Products [Member] | Commercial Specialty Business Segment [Member]
Major Product Revenue By Segment [Line Items]
Insurance Services Revenue	$ 91	$ 85	$ 176	$ 176