SEGMENT INFORMATION - Segment Results (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Premiums	$ 18,556	$ 15,776	$ 36,918	$ 31,427
Services revenue	450	355	874	710
Total external revenues	19,006	16,131	37,792	32,137
Intersegment revenues	0	0	0	0
Investment income	77	114	226	215
Total revenues	19,083	16,245	38,018	32,352
Benefits	14,175	13,318	29,804	26,811
Operating costs	2,354	1,703	4,471	3,363
Depreciation and amortization	119	109	234	216
Total operating expenses	16,648	15,130	34,509	30,390
Income from operations	2,435	1,115	3,509	1,962
Interest expense	76	60	136	122
Other (income) expense, net	(227)	(174)	70	(135)
Income before income taxes and equity in net earnings	2,586	1,229	3,303	1,975
Equity in net earnings	25	12	33	15
Segment earnings	2,611	1,241	3,336	1,990
Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	13,005	10,793	25,799	21,502
Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,976	1,626	3,987	3,258
Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	731	818	1,486	1,627
Total Medicare
Segment Reporting Information [Line Items]
Premiums	15,712	13,237	31,272	26,387
Fully-insured
Segment Reporting Information [Line Items]
Premiums	1,377	1,428	2,769	2,879
Specialty
Segment Reporting Information [Line Items]
Premiums	425	387	854	760
Medicaid and other
Segment Reporting Information [Line Items]
Premiums	1,042	724	2,023	1,401
Provider
Segment Reporting Information [Line Items]
Services revenue	105	111	209	231
ASO and other
Segment Reporting Information [Line Items]
Services revenue	198	198	397	397
Pharmacy
Segment Reporting Information [Line Items]
Services revenue	147	46	268	82
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	16,923	14,105	33,627	28,072
Services revenue	6	5	10	10
Total external revenues	16,929	14,110	33,637	28,082
Intersegment revenues	0	0	0	0
Investment income	32	48	86	89
Total revenues	16,961	14,158	33,723	28,171
Benefits	13,251	12,019	27,715	24,346
Operating costs	1,638	1,206	3,170	2,354
Depreciation and amortization	83	77	164	150
Total operating expenses	14,972	13,302	31,049	26,850
Income from operations	1,989	856	2,674	1,321
Interest expense	0	0	0	0
Other (income) expense, net	0	0	0	0
Income before income taxes and equity in net earnings	1,989	856	2,674	1,321
Equity in net earnings	0	0	0	0
Segment earnings	1,989	856	2,674	1,321
Operating Segments | Retail | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	13,005	10,793	25,799	21,502
Operating Segments | Retail | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,976	1,626	3,987	3,258
Operating Segments | Retail | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	731	818	1,486	1,627
Operating Segments | Retail | Total Medicare
Segment Reporting Information [Line Items]
Premiums	15,712	13,237	31,272	26,387
Operating Segments | Retail | Fully-insured
Segment Reporting Information [Line Items]
Premiums	169	144	332	284
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	1,042	724	2,023	1,401
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	6	5	10	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	1,633	1,671	3,291	3,355
Services revenue	192	193	387	387
Total external revenues	1,825	1,864	3,678	3,742
Intersegment revenues	6	5	13	9
Investment income	4	5	9	10
Total revenues	1,835	1,874	3,700	3,761
Benefits	1,094	1,442	2,405	2,729
Operating costs	435	406	864	819
Depreciation and amortization	19	21	39	43
Total operating expenses	1,548	1,869	3,308	3,591
Income from operations	287	5	392	170
Interest expense	0	0	0	0
Other (income) expense, net	0	0	0	0
Income before income taxes and equity in net earnings	287	5	392	170
Equity in net earnings	0	0	0	0
Segment earnings	287	5	392	170
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	1,208	1,284	2,437	2,595
Operating Segments | Group and Specialty | Specialty
Segment Reporting Information [Line Items]
Premiums	425	387	854	760
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	192	193	387	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	6	5	13	9
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	252	157	477	313
Total external revenues	252	157	477	313
Intersegment revenues	6,689	6,229	13,549	12,171
Investment income	0	1	0	1
Total revenues	6,941	6,387	14,026	12,485
Benefits	0	0	0	0
Operating costs	6,603	6,135	13,403	12,023
Depreciation and amortization	46	40	89	78
Total operating expenses	6,649	6,175	13,492	12,101
Income from operations	292	212	534	384
Interest expense	0	0	0	0
Other (income) expense, net	0	0	0	0
Income before income taxes and equity in net earnings	292	212	534	384
Equity in net earnings	25	12	33	15
Segment earnings	317	224	567	399
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	105	111	209	231
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	147	46	268	82
Operating Segments | Healthcare Services | Services
Segment Reporting Information [Line Items]
Intersegment revenues	4,712	4,496	9,662	8,802
Operating Segments | Healthcare Services | Products
Segment Reporting Information [Line Items]
Intersegment revenues	1,977	1,733	3,887	3,369
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	(6,695)	(6,234)	(13,562)	(12,180)
Investment income	41	60	131	115
Total revenues	(6,654)	(6,174)	(13,431)	(12,065)
Benefits	(170)	(143)	(316)	(264)
Operating costs	(6,322)	(6,044)	(12,966)	(11,833)
Depreciation and amortization	(29)	(29)	(58)	(55)
Total operating expenses	(6,521)	(6,216)	(13,340)	(12,152)
Income from operations	(133)	42	(91)	87
Interest expense	76	60	136	122
Other (income) expense, net	(227)	(174)	70	(135)
Income before income taxes and equity in net earnings	18	156	(297)	100
Equity in net earnings	0	0	0	0
Segment earnings	18	156	(297)	100
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	(4,718)	(4,501)	(9,675)	(8,811)
Eliminations/ Corporate | Products
Segment Reporting Information [Line Items]
Intersegment revenues	$ (1,977)	$ (1,733)	$ (3,887)	$ (3,369)