SEGMENT INFORMATION - Segment Results (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Premiums	$ 18,362	$ 15,651
Services revenue	424	355
Total external revenues	18,786	16,006
Intersegment revenues	0	0
Investment income	149	101
Total revenues	18,935	16,107
Benefits	15,629	13,493
Operating costs	2,117	1,660
Depreciation and amortization	115	107
Total operating expenses	17,861	15,260
Income from operations	1,074	847
Interest expense	60	62
Other expense, net	297	39
Income before income taxes and equity in net earnings	717	746
Equity in net earnings	8	3
Segment earnings (loss)	725	749
Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	12,794	10,709
Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	2,011	1,632
Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	755	809
Total Medicare
Segment Reporting Information [Line Items]
Premiums	15,560	13,150
Fully-insured
Segment Reporting Information [Line Items]
Premiums	1,392	1,451
Specialty
Segment Reporting Information [Line Items]
Premiums	429	373
Medicaid and other
Segment Reporting Information [Line Items]
Premiums	981	677
Provider
Segment Reporting Information [Line Items]
Services revenue	104	120
ASO and other
Segment Reporting Information [Line Items]
Services revenue	199	199
Pharmacy
Segment Reporting Information [Line Items]
Services revenue	121	36
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	16,704	13,967
Services revenue	4	5
Total external revenues	16,708	13,972
Intersegment revenues	0	0
Investment income	54	41
Total revenues	16,762	14,013
Benefits	14,464	12,327
Operating costs	1,532	1,148
Depreciation and amortization	81	73
Total operating expenses	16,077	13,548
Income from operations	685	465
Interest expense	0	0
Other expense, net	0	0
Income before income taxes and equity in net earnings	685	465
Equity in net earnings	0	0
Segment earnings (loss)	685	465
Operating Segments | Retail | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	12,794	10,709
Operating Segments | Retail | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	2,011	1,632
Operating Segments | Retail | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	755	809
Operating Segments | Retail | Total Medicare
Segment Reporting Information [Line Items]
Premiums	15,560	13,150
Operating Segments | Retail | Fully-insured
Segment Reporting Information [Line Items]
Premiums	163	140
Operating Segments | Retail | Specialty
Segment Reporting Information [Line Items]
Premiums	0	0
Operating Segments | Retail | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	981	677
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	4	5
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	1,658	1,684
Services revenue	195	194
Total external revenues	1,853	1,878
Intersegment revenues	7	4
Investment income	5	5
Total revenues	1,865	1,887
Benefits	1,311	1,287
Operating costs	429	413
Depreciation and amortization	20	22
Total operating expenses	1,760	1,722
Income from operations	105	165
Interest expense	0	0
Other expense, net	0	0
Income before income taxes and equity in net earnings	105	165
Equity in net earnings	0	0
Segment earnings (loss)	105	165
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	1,229	1,311
Operating Segments | Group and Specialty | Specialty
Segment Reporting Information [Line Items]
Premiums	429	373
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	195	194
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	7	4
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	225	156
Total external revenues	225	156
Intersegment revenues	6,860	5,942
Investment income	0	0
Total revenues	7,085	6,098
Benefits	0	0
Operating costs	6,800	5,888
Depreciation and amortization	43	38
Total operating expenses	6,843	5,926
Income from operations	242	172
Interest expense	0	0
Other expense, net	0	0
Income before income taxes and equity in net earnings	242	172
Equity in net earnings	8	3
Segment earnings (loss)	250	175
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	104	120
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	121	36
Operating Segments | Healthcare Services | Services
Segment Reporting Information [Line Items]
Intersegment revenues	4,950	4,306
Operating Segments | Healthcare Services | Products
Segment Reporting Information [Line Items]
Intersegment revenues	1,910	1,636
Eliminations/ Corporate
Segment Reporting Information [Line Items]
Premiums	0	0
Services revenue	0	0
Total external revenues	0	0
Intersegment revenues	(6,867)	(5,946)
Investment income	90	55
Total revenues	(6,777)	(5,891)
Benefits	(146)	(121)
Operating costs	(6,644)	(5,789)
Depreciation and amortization	(29)	(26)
Total operating expenses	(6,819)	(5,936)
Income from operations	42	45
Interest expense	60	62
Other expense, net	297	39
Income before income taxes and equity in net earnings	(315)	(56)
Equity in net earnings	0	0
Segment earnings (loss)	(315)	(56)
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	(4,957)	(4,310)
Eliminations/ Corporate | Products
Segment Reporting Information [Line Items]
Intersegment revenues	$ (1,910)	$ (1,636)