Segment Information (Financial Data By Reportable Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Reportable segments operating revenues	$ 30,649	$ 26,444	$ 89,275	$ 76,009
Operating gain (loss)	201	1,528	5,755	4,901
Commercial & Specialty [Member]
Segment Reporting Information [Line Items]
Operating gain (loss)	(234)	924	2,558	3,505
Government Business [Member]
Segment Reporting Information [Line Items]
Operating gain (loss)	246	616	2,275	1,470
IngenioRx Segment [Member]
Segment Reporting Information [Line Items]
Operating gain (loss)	345	0	998	0
Other [Member]
Segment Reporting Information [Line Items]
Operating gain (loss)	(156)	(12)	(76)	(74)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	(4,158)	(1,303)	(11,335)	(2,353)
Unaffiliated
Segment Reporting Information [Line Items]
Reportable segments operating revenues	30,649	26,444	89,275	76,009
Unaffiliated | Commercial & Specialty [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	9,326	9,284	27,476	28,093
Unaffiliated | Government Business [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	18,101	15,955	52,809	46,419
Unaffiliated | IngenioRx Segment [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	2,598	774	7,485	880
Unaffiliated | Other [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	624	431	1,505	617
Affiliated [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	0	0	0	0
Affiliated [Member] | Commercial & Specialty [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues		0	0	0
Affiliated [Member] | Government Business [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues		0	0	0
Affiliated [Member] | IngenioRx Segment [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	2,984	1,148	8,563	1,290
Affiliated [Member] | Other [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	$ 1,174	$ 155	$ 2,772	$ 1,063