SEGMENT INFORMATION - Segment Results (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Premiums	$ 19,978	$ 18,556	$ 40,102	$ 36,918
Services revenue	491	450	957	874
Total external revenues	20,469	19,006	41,059	37,792
Intersegment revenues	0	0	0	0
Investment income	176	77	254	226
Total revenues	20,645	19,083	41,313	38,018
Benefits	17,149	14,175	34,445	29,804
Operating costs	2,116	2,354	4,123	4,471
Depreciation and amortization	144	119	286	234
Total operating expenses	19,409	16,648	38,854	34,509
Income from operations	1,236	2,435	2,459	3,509
Interest expense	79	76	147	136
Other expense (income), net	419	(227)	534	70
Income before income taxes and equity in net earnings	738	2,586	1,778	3,303
Equity in net earnings	33	25	54	33
Segment earnings (loss)	771	2,611	1,832	3,336
Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	14,585	13,005	29,400	25,799
Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,775	1,976	3,530	3,987
Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	662	731	1,326	1,486
Total Medicare
Segment Reporting Information [Line Items]
Premiums	17,022	15,712	34,256	31,272
Fully-insured
Segment Reporting Information [Line Items]
Premiums	1,260	1,377	2,537	2,769
Specialty
Segment Reporting Information [Line Items]
Premiums	432	425	866	854
Medicaid and other
Segment Reporting Information [Line Items]
Premiums	1,264	1,042	2,443	2,023
Provider
Segment Reporting Information [Line Items]
Services revenue	122	105	237	209
ASO and other
Segment Reporting Information [Line Items]
Services revenue	206	198	401	397
Pharmacy
Segment Reporting Information [Line Items]
Services revenue	163	147	319	268
Services
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0	0
Products
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0	0
Operating segments | Retail
Segment Reporting Information [Line Items]
Premiums	18,468	16,923	37,059	33,627
Services revenue	12	6	17	10
Total external revenues	18,480	16,929	37,076	33,637
Intersegment revenues	0	0	0	0
Investment income	65	32	117	86
Total revenues	18,545	16,961	37,193	33,723
Benefits	16,068	13,251	32,367	27,715
Operating costs	1,533	1,638	2,984	3,170
Depreciation and amortization	108	83	212	164
Total operating expenses	17,709	14,972	35,563	31,049
Income from operations	836	1,989	1,630	2,674
Interest expense	0	0	0	0
Other expense (income), net	0	0	0	0
Income before income taxes and equity in net earnings	836	1,989	1,630	2,674
Equity in net earnings	0	0	0	0
Segment earnings (loss)	836	1,989	1,630	2,674
Operating segments | Retail | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	14,585	13,005	29,400	25,799
Operating segments | Retail | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,775	1,976	3,530	3,987
Operating segments | Retail | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	662	731	1,326	1,486
Operating segments | Retail | Total Medicare
Segment Reporting Information [Line Items]
Premiums	17,022	15,712	34,256	31,272
Operating segments | Retail | Fully-insured
Segment Reporting Information [Line Items]
Premiums	182	169	360	332
Operating segments | Retail | Specialty
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating segments | Retail | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	1,264	1,042	2,443	2,023
Operating segments | Retail | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Operating segments | Retail | ASO and other
Segment Reporting Information [Line Items]
Services revenue	12	6	17	10
Operating segments | Retail | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Operating segments | Retail | Services
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0	0
Operating segments | Retail | Products
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0	0
Operating segments | Group and Specialty
Segment Reporting Information [Line Items]
Premiums	1,510	1,633	3,043	3,291
Services revenue	194	192	384	387
Total external revenues	1,704	1,825	3,427	3,678
Intersegment revenues	10	6	20	13
Investment income	4	4	8	9
Total revenues	1,718	1,835	3,455	3,700
Benefits	1,247	1,094	2,392	2,405
Operating costs	409	435	806	864
Depreciation and amortization	22	19	43	39
Total operating expenses	1,678	1,548	3,241	3,308
Income from operations	40	287	214	392
Interest expense	0	0	0	0
Other expense (income), net	0	0	0	0
Income before income taxes and equity in net earnings	40	287	214	392
Equity in net earnings	0	0	0	0
Segment earnings (loss)	40	287	214	392
Operating segments | Group and Specialty | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating segments | Group and Specialty | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating segments | Group and Specialty | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating segments | Group and Specialty | Total Medicare
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating segments | Group and Specialty | Fully-insured
Segment Reporting Information [Line Items]
Premiums	1,078	1,208	2,177	2,437
Operating segments | Group and Specialty | Specialty
Segment Reporting Information [Line Items]
Premiums	432	425	866	854
Operating segments | Group and Specialty | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating segments | Group and Specialty | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Operating segments | Group and Specialty | ASO and other
Segment Reporting Information [Line Items]
Services revenue	194	192	384	387
Operating segments | Group and Specialty | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Operating segments | Group and Specialty | Services
Segment Reporting Information [Line Items]
Intersegment revenues	10	6	20	13
Operating segments | Group and Specialty | Products
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0	0
Operating segments | Healthcare Services
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Services revenue	285	252	556	477
Total external revenues	285	252	556	477
Intersegment revenues	7,238	6,689	14,164	13,549
Investment income	1	0	2	0
Total revenues	7,524	6,941	14,722	14,026
Benefits	0	0	0	0
Operating costs	7,205	6,603	14,115	13,403
Depreciation and amortization	41	46	81	89
Total operating expenses	7,246	6,649	14,196	13,492
Income from operations	278	292	526	534
Interest expense	0	0	0	0
Other expense (income), net	0	0	0	0
Income before income taxes and equity in net earnings	278	292	526	534
Equity in net earnings	33	25	54	33
Segment earnings (loss)	311	317	580	567
Operating segments | Healthcare Services | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating segments | Healthcare Services | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating segments | Healthcare Services | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating segments | Healthcare Services | Total Medicare
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating segments | Healthcare Services | Fully-insured
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating segments | Healthcare Services | Specialty
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating segments | Healthcare Services | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating segments | Healthcare Services | Provider
Segment Reporting Information [Line Items]
Services revenue	122	105	237	209
Operating segments | Healthcare Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Operating segments | Healthcare Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	163	147	319	268
Operating segments | Healthcare Services | Services
Segment Reporting Information [Line Items]
Intersegment revenues	4,977	4,712	9,751	9,662
Operating segments | Healthcare Services | Products
Segment Reporting Information [Line Items]
Intersegment revenues	2,261	1,977	4,413	3,887
Eliminations/ Corporate
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Services revenue	0	0	0	0
Total external revenues	0	0	0	0
Intersegment revenues	(7,248)	(6,695)	(14,184)	(13,562)
Investment income	106	41	127	131
Total revenues	(7,142)	(6,654)	(14,057)	(13,431)
Benefits	(166)	(170)	(314)	(316)
Operating costs	(7,031)	(6,322)	(13,782)	(12,966)
Depreciation and amortization	(27)	(29)	(50)	(58)
Total operating expenses	(7,224)	(6,521)	(14,146)	(13,340)
Income from operations	82	(133)	89	(91)
Interest expense	79	76	147	136
Other expense (income), net	419	(227)	534	70
Income before income taxes and equity in net earnings	(416)	18	(592)	(297)
Equity in net earnings	0	0	0	0
Segment earnings (loss)	(416)	18	(592)	(297)
Eliminations/ Corporate | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Eliminations/ Corporate | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Eliminations/ Corporate | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Eliminations/ Corporate | Total Medicare
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Eliminations/ Corporate | Fully-insured
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Eliminations/ Corporate | Specialty
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Eliminations/ Corporate | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Eliminations/ Corporate | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Eliminations/ Corporate | ASO and other
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Eliminations/ Corporate | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Eliminations/ Corporate | Services
Segment Reporting Information [Line Items]
Intersegment revenues	(4,987)	(4,718)	(9,771)	(9,675)
Eliminations/ Corporate | Products
Segment Reporting Information [Line Items]
Intersegment revenues	$ (2,261)	$ (1,977)	$ (4,413)	$ (3,887)