SEGMENT INFORMATION - Segment Results (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Premiums	$ 74,186	$ 62,948	$ 54,941
Services revenue	1,815	1,439	1,457
Total external revenues	76,001	64,387	56,398
Intersegment revenues	0	0	0
Investment income	1,154	501	514
Total revenues	77,155	64,888	56,912
Benefits	61,628	53,857	45,882
Operating costs	10,052	7,381	7,525
Depreciation and amortization	489	458	405
Total operating expenses	72,169	61,696	53,812
Income from operations	4,986	3,192	3,100
Loss on sale of business	0	0	786
Interest expense	283	242	218
Other expense (income), net	103	(506)	33
Income before income taxes and equity in net earnings	4,600	3,456	2,063
Equity in net earnings	74	14	11
Segment earnings (loss)	4,674	3,470	2,074
Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	51,697	43,128	35,656
Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	7,774	6,475	6,103
Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	2,742	3,165	3,584
Total Medicare
Segment Reporting Information [Line Items]
Premiums	62,213	52,768	45,343
Fully-insured
Segment Reporting Information [Line Items]
Premiums	6,051	5,711	5,962
Specialty
Segment Reporting Information [Line Items]
Premiums	1,699	1,571	1,359
Medicaid and other
Segment Reporting Information [Line Items]
Premiums	4,223	2,898	2,277
Provider
Segment Reporting Information [Line Items]
Services revenue	435	446	404
ASO and other
Segment Reporting Information [Line Items]
Services revenue	799	807	850
Pharmacy
Segment Reporting Information [Line Items]
Services revenue	581	186	203
Services
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0
Products
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0
Operating Segments | Retail
Segment Reporting Information [Line Items]
Premiums	67,124	56,254	48,108
Services revenue	19	17	11
Total external revenues	67,143	56,271	48,119
Intersegment revenues	0	0	0
Investment income	155	195	136
Total revenues	67,298	56,466	48,255
Benefits	56,537	48,602	40,925
Operating costs	7,402	5,306	5,327
Depreciation and amortization	342	323	270
Total operating expenses	64,281	54,231	46,522
Income from operations	3,017	2,235	1,733
Loss on sale of business			0
Interest expense	0	0	0
Other expense (income), net	0	0	0
Income before income taxes and equity in net earnings	3,017	2,235	1,733
Equity in net earnings	0	0	0
Segment earnings (loss)	3,017	2,235	1,733
Operating Segments | Retail | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	51,697	43,128	35,656
Operating Segments | Retail | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	7,774	6,475	6,103
Operating Segments | Retail | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	2,742	3,165	3,584
Operating Segments | Retail | Total Medicare
Segment Reporting Information [Line Items]
Premiums	62,213	52,768	45,343
Operating Segments | Retail | Fully-insured
Segment Reporting Information [Line Items]
Premiums	688	588	510
Operating Segments | Retail | Specialty
Segment Reporting Information [Line Items]
Premiums	0	0	0
Operating Segments | Retail | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	4,223	2,898	2,255
Operating Segments | Retail | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0	0
Operating Segments | Retail | ASO and other
Segment Reporting Information [Line Items]
Services revenue	19	17	11
Operating Segments | Retail | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0	0
Operating Segments | Retail | Services
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0
Operating Segments | Retail | Products
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0
Operating Segments | Group and Specialty
Segment Reporting Information [Line Items]
Premiums	6,460	6,694	6,803
Services revenue	780	790	835
Total external revenues	7,240	7,484	7,638
Intersegment revenues	29	18	18
Investment income	16	23	23
Total revenues	7,285	7,525	7,679
Benefits	5,529	5,758	5,420
Operating costs	1,818	1,651	1,810
Depreciation and amortization	81	88	88
Total operating expenses	7,428	7,497	7,318
Income from operations	(143)	28	361
Loss on sale of business			0
Interest expense	0	0	0
Other expense (income), net	0	0	0
Income before income taxes and equity in net earnings	(143)	28	361
Equity in net earnings	0	0	0
Segment earnings (loss)	(143)	28	361
Operating Segments | Group and Specialty | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0
Operating Segments | Group and Specialty | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0
Operating Segments | Group and Specialty | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	0	0	0
Operating Segments | Group and Specialty | Total Medicare
Segment Reporting Information [Line Items]
Premiums	0	0	0
Operating Segments | Group and Specialty | Fully-insured
Segment Reporting Information [Line Items]
Premiums	4,761	5,123	5,444
Operating Segments | Group and Specialty | Specialty
Segment Reporting Information [Line Items]
Premiums	1,699	1,571	1,359
Operating Segments | Group and Specialty | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	0	0	0
Operating Segments | Group and Specialty | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0	0
Operating Segments | Group and Specialty | ASO and other
Segment Reporting Information [Line Items]
Services revenue	780	790	835
Operating Segments | Group and Specialty | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0	0
Operating Segments | Group and Specialty | Services
Segment Reporting Information [Line Items]
Intersegment revenues	29	18	18
Operating Segments | Group and Specialty | Products
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0
Operating Segments | Healthcare Services
Segment Reporting Information [Line Items]
Premiums	0	0	0
Services revenue	1,016	632	607
Total external revenues	1,016	632	607
Intersegment revenues	27,419	25,149	23,170
Investment income	13	2	34
Total revenues	28,448	25,783	23,811
Benefits	0	0	0
Operating costs	27,395	24,852	22,905
Depreciation and amortization	183	156	163
Total operating expenses	27,578	25,008	23,068
Income from operations	870	775	743
Loss on sale of business			0
Interest expense	0	0	0
Other expense (income), net	0	0	0
Income before income taxes and equity in net earnings	870	775	743
Equity in net earnings	74	14	11
Segment earnings (loss)	944	789	754
Operating Segments | Healthcare Services | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0
Operating Segments | Healthcare Services | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0
Operating Segments | Healthcare Services | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	0	0	0
Operating Segments | Healthcare Services | Total Medicare
Segment Reporting Information [Line Items]
Premiums	0	0	0
Operating Segments | Healthcare Services | Fully-insured
Segment Reporting Information [Line Items]
Premiums	0	0	0
Operating Segments | Healthcare Services | Specialty
Segment Reporting Information [Line Items]
Premiums	0	0	0
Operating Segments | Healthcare Services | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	0	0	0
Operating Segments | Healthcare Services | Provider
Segment Reporting Information [Line Items]
Services revenue	435	446	404
Operating Segments | Healthcare Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue	0	0	0
Operating Segments | Healthcare Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	581	186	203
Operating Segments | Healthcare Services | Services
Segment Reporting Information [Line Items]
Intersegment revenues	19,491	18,255	16,840
Operating Segments | Healthcare Services | Products
Segment Reporting Information [Line Items]
Intersegment revenues	7,928	6,894	6,330
Operating Segments | Individual Commercial
Segment Reporting Information [Line Items]
Premiums			8
Services revenue			0
Total external revenues			8
Intersegment revenues			0
Investment income			0
Total revenues			8
Benefits			(70)
Operating costs			4
Depreciation and amortization			0
Total operating expenses			(66)
Income from operations			74
Loss on sale of business			0
Interest expense			0
Other expense (income), net			0
Income before income taxes and equity in net earnings			74
Equity in net earnings			0
Segment earnings (loss)			74
Operating Segments | Individual Commercial | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums			0
Operating Segments | Individual Commercial | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums			0
Operating Segments | Individual Commercial | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums			0
Operating Segments | Individual Commercial | Total Medicare
Segment Reporting Information [Line Items]
Premiums			0
Operating Segments | Individual Commercial | Fully-insured
Segment Reporting Information [Line Items]
Premiums			8
Operating Segments | Individual Commercial | Specialty
Segment Reporting Information [Line Items]
Premiums			0
Operating Segments | Individual Commercial | Medicaid and other
Segment Reporting Information [Line Items]
Premiums			0
Operating Segments | Individual Commercial | Provider
Segment Reporting Information [Line Items]
Services revenue			0
Operating Segments | Individual Commercial | ASO and other
Segment Reporting Information [Line Items]
Services revenue			0
Operating Segments | Individual Commercial | Pharmacy
Segment Reporting Information [Line Items]
Services revenue			0
Operating Segments | Individual Commercial | Services
Segment Reporting Information [Line Items]
Intersegment revenues			0
Operating Segments | Individual Commercial | Products
Segment Reporting Information [Line Items]
Intersegment revenues			0
Other Businesses
Segment Reporting Information [Line Items]
Premiums			22
Services revenue			4
Total external revenues			26
Intersegment revenues			0
Investment income			110
Total revenues			136
Benefits			77
Operating costs			6
Depreciation and amortization			0
Total operating expenses			83
Income from operations			53
Loss on sale of business			0
Interest expense			0
Other expense (income), net			0
Income before income taxes and equity in net earnings			53
Equity in net earnings			0
Segment earnings (loss)			53
Other Businesses | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums			0
Other Businesses | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums			0
Other Businesses | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums			0
Other Businesses | Total Medicare
Segment Reporting Information [Line Items]
Premiums			0
Other Businesses | Fully-insured
Segment Reporting Information [Line Items]
Premiums			0
Other Businesses | Specialty
Segment Reporting Information [Line Items]
Premiums			0
Other Businesses | Medicaid and other
Segment Reporting Information [Line Items]
Premiums			22
Other Businesses | Provider
Segment Reporting Information [Line Items]
Services revenue			0
Other Businesses | ASO and other
Segment Reporting Information [Line Items]
Services revenue			4
Other Businesses | Pharmacy
Segment Reporting Information [Line Items]
Services revenue			0
Other Businesses | Services
Segment Reporting Information [Line Items]
Intersegment revenues			0
Other Businesses | Products
Segment Reporting Information [Line Items]
Intersegment revenues			0
Eliminations/Corporate
Segment Reporting Information [Line Items]
Premiums	602	0	0
Services revenue	0	0	0
Total external revenues	602	0	0
Intersegment revenues	(27,448)	(25,167)	(23,188)
Investment income	970	281	211
Total revenues	(25,876)	(24,886)	(22,977)
Benefits	(438)	(503)	(470)
Operating costs	(26,563)	(24,428)	(22,527)
Depreciation and amortization	(117)	(109)	(116)
Total operating expenses	(27,118)	(25,040)	(23,113)
Income from operations	1,242	154	136
Loss on sale of business			786
Interest expense	283	242	218
Other expense (income), net	103	(506)	33
Income before income taxes and equity in net earnings	856	418	(901)
Equity in net earnings	0	0	0
Segment earnings (loss)	856	418	(901)
Eliminations/Corporate | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0
Eliminations/Corporate | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0
Eliminations/Corporate | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	0	0	0
Eliminations/Corporate | Total Medicare
Segment Reporting Information [Line Items]
Premiums	0	0	0
Eliminations/Corporate | Fully-insured
Segment Reporting Information [Line Items]
Premiums	602	0	0
Eliminations/Corporate | Specialty
Segment Reporting Information [Line Items]
Premiums	0	0	0
Eliminations/Corporate | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	0	0	0
Eliminations/Corporate | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0	0
Eliminations/Corporate | ASO and other
Segment Reporting Information [Line Items]
Services revenue	0	0	0
Eliminations/Corporate | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0	0
Eliminations/Corporate | Services
Segment Reporting Information [Line Items]
Intersegment revenues	(19,520)	(18,273)	(16,858)
Eliminations/Corporate | Products
Segment Reporting Information [Line Items]
Intersegment revenues	$ (7,928)	$ (6,894)	$ (6,330)