SEGMENT INFORMATION - Segment Results (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Premiums	$ 20,124	$ 18,362
Services revenue	466	424
Total external revenues	20,590	18,786
Intersegment revenues	0	0
Investment income	78	149
Total revenues	20,668	18,935
Benefits	17,296	15,629
Operating costs	2,007	2,117
Depreciation and amortization	142	115
Total operating expenses	19,445	17,861
Income from operations	1,223	1,074
Interest expense	68	60
Other expense, net	115	297
Income before income taxes and equity in net earnings	1,040	717
Equity in net earnings	21	8
Segment earnings (loss)	1,061	725
Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	14,815	12,794
Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,755	2,011
Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	664	755
Total Medicare
Segment Reporting Information [Line Items]
Premiums	17,234	15,560
Fully-insured
Segment Reporting Information [Line Items]
Premiums	1,277	1,392
Specialty
Segment Reporting Information [Line Items]
Premiums	434	429
Medicaid and other
Segment Reporting Information [Line Items]
Premiums	1,179	981
Provider
Segment Reporting Information [Line Items]
Services revenue	115	104
ASO and other
Segment Reporting Information [Line Items]
Services revenue	195	199
Pharmacy
Segment Reporting Information [Line Items]
Services revenue	156	121
Services
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Products
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Operating segments | Retail
Segment Reporting Information [Line Items]
Premiums	18,591	16,704
Services revenue	5	4
Total external revenues	18,596	16,708
Intersegment revenues	0	0
Investment income	52	54
Total revenues	18,648	16,762
Benefits	16,299	14,464
Operating costs	1,451	1,532
Depreciation and amortization	104	81
Total operating expenses	17,854	16,077
Income from operations	794	685
Interest expense	0	0
Other expense, net	0	0
Income before income taxes and equity in net earnings	794	685
Equity in net earnings	0	0
Segment earnings (loss)	794	685
Operating segments | Retail | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	14,815	12,794
Operating segments | Retail | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,755	2,011
Operating segments | Retail | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	664	755
Operating segments | Retail | Total Medicare
Segment Reporting Information [Line Items]
Premiums	17,234	15,560
Operating segments | Retail | Fully-insured
Segment Reporting Information [Line Items]
Premiums	178	163
Operating segments | Retail | Specialty
Segment Reporting Information [Line Items]
Premiums	0	0
Operating segments | Retail | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	1,179	981
Operating segments | Retail | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0
Operating segments | Retail | ASO and other
Segment Reporting Information [Line Items]
Services revenue	5	4
Operating segments | Retail | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0
Operating segments | Retail | Services
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Operating segments | Retail | Products
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Operating segments | Group and Specialty
Segment Reporting Information [Line Items]
Premiums	1,533	1,658
Services revenue	190	195
Total external revenues	1,723	1,853
Intersegment revenues	10	7
Investment income	4	5
Total revenues	1,737	1,865
Benefits	1,145	1,311
Operating costs	397	429
Depreciation and amortization	21	20
Total operating expenses	1,563	1,760
Income from operations	174	105
Interest expense	0	0
Other expense, net	0	0
Income before income taxes and equity in net earnings	174	105
Equity in net earnings	0	0
Segment earnings (loss)	174	105
Operating segments | Group and Specialty | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0
Operating segments | Group and Specialty | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0
Operating segments | Group and Specialty | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	0	0
Operating segments | Group and Specialty | Total Medicare
Segment Reporting Information [Line Items]
Premiums	0	0
Operating segments | Group and Specialty | Fully-insured
Segment Reporting Information [Line Items]
Premiums	1,099	1,229
Operating segments | Group and Specialty | Specialty
Segment Reporting Information [Line Items]
Premiums	434	429
Operating segments | Group and Specialty | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	0	0
Operating segments | Group and Specialty | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0
Operating segments | Group and Specialty | ASO and other
Segment Reporting Information [Line Items]
Services revenue	190	195
Operating segments | Group and Specialty | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0
Operating segments | Group and Specialty | Services
Segment Reporting Information [Line Items]
Intersegment revenues	10	7
Operating segments | Group and Specialty | Products
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Operating segments | Healthcare Services
Segment Reporting Information [Line Items]
Premiums	0	0
Services revenue	271	225
Total external revenues	271	225
Intersegment revenues	6,926	6,860
Investment income	1	0
Total revenues	7,198	7,085
Benefits	0	0
Operating costs	6,910	6,800
Depreciation and amortization	40	43
Total operating expenses	6,950	6,843
Income from operations	248	242
Interest expense	0	0
Other expense, net	0	0
Income before income taxes and equity in net earnings	248	242
Equity in net earnings	21	8
Segment earnings (loss)	269	250
Operating segments | Healthcare Services | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0
Operating segments | Healthcare Services | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0
Operating segments | Healthcare Services | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	0	0
Operating segments | Healthcare Services | Total Medicare
Segment Reporting Information [Line Items]
Premiums	0	0
Operating segments | Healthcare Services | Fully-insured
Segment Reporting Information [Line Items]
Premiums	0	0
Operating segments | Healthcare Services | Specialty
Segment Reporting Information [Line Items]
Premiums	0	0
Operating segments | Healthcare Services | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	0	0
Operating segments | Healthcare Services | Provider
Segment Reporting Information [Line Items]
Services revenue	115	104
Operating segments | Healthcare Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue	0	0
Operating segments | Healthcare Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	156	121
Operating segments | Healthcare Services | Services
Segment Reporting Information [Line Items]
Intersegment revenues	4,774	4,950
Operating segments | Healthcare Services | Products
Segment Reporting Information [Line Items]
Intersegment revenues	2,152	1,910
Eliminations/ Corporate
Segment Reporting Information [Line Items]
Premiums	0	0
Services revenue	0	0
Total external revenues	0	0
Intersegment revenues	(6,936)	(6,867)
Investment income	21	90
Total revenues	(6,915)	(6,777)
Benefits	(148)	(146)
Operating costs	(6,751)	(6,644)
Depreciation and amortization	(23)	(29)
Total operating expenses	(6,922)	(6,819)
Income from operations	7	42
Interest expense	68	60
Other expense, net	115	297
Income before income taxes and equity in net earnings	(176)	(315)
Equity in net earnings	0	0
Segment earnings (loss)	(176)	(315)
Eliminations/ Corporate | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0
Eliminations/ Corporate | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0
Eliminations/ Corporate | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	0	0
Eliminations/ Corporate | Total Medicare
Segment Reporting Information [Line Items]
Premiums	0	0
Eliminations/ Corporate | Fully-insured
Segment Reporting Information [Line Items]
Premiums	0	0
Eliminations/ Corporate | Specialty
Segment Reporting Information [Line Items]
Premiums	0	0
Eliminations/ Corporate | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	0	0
Eliminations/ Corporate | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0
Eliminations/ Corporate | ASO and other
Segment Reporting Information [Line Items]
Services revenue	0	0
Eliminations/ Corporate | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0
Eliminations/ Corporate | Services
Segment Reporting Information [Line Items]
Intersegment revenues	(4,784)	(4,957)
Eliminations/ Corporate | Products
Segment Reporting Information [Line Items]
Intersegment revenues	$ (2,152)	$ (1,910)