SEGMENT INFORMATION - Segment Results (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]
Premiums	$ 18,904	$ 15,712	$ 55,822	$ 47,139
Services revenue	457	393	1,331	1,103
Total external revenues	19,361	16,105	57,153	48,242
Intersegment revenues	0	0	0	0
Investment income	714	136	940	351
Total revenues	20,075	16,241	58,093	48,593
Benefits	15,611	13,357	45,415	40,168
Operating costs	2,513	1,889	6,984	5,252
Depreciation and amortization	128	127	362	343
Total operating expenses	18,252	15,373	52,761	45,763
Income from operations	1,823	868	5,332	2,830
Interest expense	75	62	211	184
Other (income) expense, net	(7)	(82)	63	(217)
Income before income taxes and equity in net earnings	1,755	888	5,058	2,863
Equity in net earnings	35	1	68	16
Segment earnings (loss)	1,790	889	5,126	2,879
Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	12,949	10,752	38,748	32,254
Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,880	1,609	5,867	4,867
Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	622	781	2,108	2,408
Total Medicare
Segment Reporting Information [Line Items]
Premiums	15,451	13,142	46,723	39,529
Fully-insured
Segment Reporting Information [Line Items]
Premiums	1,948	1,428	4,717	4,307
Specialty
Segment Reporting Information [Line Items]
Premiums	424	400	1,278	1,160
Medicaid and other
Segment Reporting Information [Line Items]
Premiums	1,081	742	3,104	2,143
Provider
Segment Reporting Information [Line Items]
Services revenue	107	136	316	367
ASO and other
Segment Reporting Information [Line Items]
Services revenue	193	204	590	601
Pharmacy
Segment Reporting Information [Line Items]
Services revenue	157	53	425	135
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	16,709	14,034	50,336	42,106
Services revenue	4	4	14	14
Total external revenues	16,713	14,038	50,350	42,120
Intersegment revenues	0	0	0	0
Investment income	28	50	114	139
Total revenues	16,741	14,088	50,464	42,259
Benefits	14,224	12,050	41,939	36,396
Operating costs	1,877	1,310	5,047	3,664
Depreciation and amortization	87	89	251	239
Total operating expenses	16,188	13,449	47,237	40,299
Income from operations	553	639	3,227	1,960
Interest expense	0	0	0	0
Other (income) expense, net	0	0	0	0
Income before income taxes and equity in net earnings	553	639	3,227	1,960
Equity in net earnings	0	0	0	0
Segment earnings (loss)	553	639	3,227	1,960
Operating Segments | Retail | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	12,949	10,752	38,748	32,254
Operating Segments | Retail | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,880	1,609	5,867	4,867
Operating Segments | Retail | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	622	781	2,108	2,408
Operating Segments | Retail | Total Medicare
Segment Reporting Information [Line Items]
Premiums	15,451	13,142	46,723	39,529
Operating Segments | Retail | Fully-insured
Segment Reporting Information [Line Items]
Premiums	177	150	509	434
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	1,081	742	3,104	2,143
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	4	4	14	14
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	1,593	1,678	4,884	5,033
Services revenue	189	200	576	587
Total external revenues	1,782	1,878	5,460	5,620
Intersegment revenues	9	4	22	13
Investment income	3	7	12	17
Total revenues	1,794	1,889	5,494	5,650
Benefits	1,481	1,448	3,886	4,177
Operating costs	452	413	1,316	1,232
Depreciation and amortization	21	24	60	67
Total operating expenses	1,954	1,885	5,262	5,476
Income from operations	(160)	4	232	174
Interest expense	0	0	0	0
Other (income) expense, net	0	0	0	0
Income before income taxes and equity in net earnings	(160)	4	232	174
Equity in net earnings	0	0	0	0
Segment earnings (loss)	(160)	4	232	174
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	1,169	1,278	3,606	3,873
Operating Segments | Group and Specialty | Specialty
Segment Reporting Information [Line Items]
Premiums	424	400	1,278	1,160
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	189	200	576	587
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	9	4	22	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	264	189	741	502
Total external revenues	264	189	741	502
Intersegment revenues	6,865	6,413	20,414	18,584
Investment income	2	0	2	1
Total revenues	7,131	6,602	21,157	19,087
Benefits	0	0	0	0
Operating costs	6,871	6,348	20,274	18,371
Depreciation and amortization	46	43	135	121
Total operating expenses	6,917	6,391	20,409	18,492
Income from operations	214	211	748	595
Interest expense	0	0	0	0
Other (income) expense, net	0	0	0	0
Income before income taxes and equity in net earnings	214	211	748	595
Equity in net earnings	35	1	68	16
Segment earnings (loss)	249	212	816	611
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	107	136	316	367
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	157	53	425	135
Operating Segments | Healthcare Services | Services
Segment Reporting Information [Line Items]
Intersegment revenues	4,852	4,654	14,514	13,456
Operating Segments | Healthcare Services | Products
Segment Reporting Information [Line Items]
Intersegment revenues	2,013	1,759	5,900	5,128
Eliminations/ Corporate
Segment Reporting Information [Line Items]
Premiums	602	0	602	0
Services revenue	0	0	0	0
Total external revenues	602	0	602	0
Intersegment revenues	(6,874)	(6,417)	(20,436)	(18,597)
Investment income	681	79	812	194
Total revenues	(5,591)	(6,338)	(19,022)	(18,403)
Benefits	(94)	(141)	(410)	(405)
Operating costs	(6,687)	(6,182)	(19,653)	(18,015)
Depreciation and amortization	(26)	(29)	(84)	(84)
Total operating expenses	(6,807)	(6,352)	(20,147)	(18,504)
Income from operations	1,216	14	1,125	101
Interest expense	75	62	211	184
Other (income) expense, net	(7)	(82)	63	(217)
Income before income taxes and equity in net earnings	1,148	34	851	134
Equity in net earnings	0	0	0	0
Segment earnings (loss)	1,148	34	851	134
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	602	0	602	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	(4,861)	(4,658)	(14,536)	(13,469)
Eliminations/ Corporate | Products
Segment Reporting Information [Line Items]
Intersegment revenues	$ (2,013)	$ (1,759)	$ (5,900)	$ (5,128)