SEGMENT INFORMATION - Segment Results (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Premiums	$ 15,651	$ 13,811
Services revenue	355	327
Investment income	101	141
Total revenues	16,107	14,279
Benefits	13,493	11,670
Operating costs	1,660	1,749
Depreciation and amortization	107	100
Total operating expenses	15,260	13,519
Income from operations	847	760
Interest expense	62	53
Other expense, net	39	0
Income before income taxes and equity in net earnings	746	707
Equity in net earnings of Kindred at Home	3	0
Segment earnings	749	707
Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	10,709	8,970
Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,632	1,524
Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	809	896
Total Medicare
Segment Reporting Information [Line Items]
Premiums	13,150	11,390
Fully-insured
Segment Reporting Information [Line Items]
Premiums	1,451	1,512
Specialty
Segment Reporting Information [Line Items]
Premiums	373	347
Medicaid and other
Segment Reporting Information [Line Items]
Premiums	677	562
Total external revenues
Segment Reporting Information [Line Items]
Total revenues	16,006	14,138
Services
Segment Reporting Information [Line Items]
Services revenue	355	327
Services | Provider
Segment Reporting Information [Line Items]
Services revenue	120	65
Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue	199	223
Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	36	39
Operating Segments | Retail
Segment Reporting Information [Line Items]
Premiums	13,967	12,068
Investment income	41	37
Total revenues	14,013	12,107
Benefits	12,327	10,552
Operating costs	1,148	1,222
Depreciation and amortization	73	66
Total operating expenses	13,548	11,840
Income from operations	465	267
Interest expense	0	0
Other expense, net	0
Income before income taxes and equity in net earnings	465	267
Equity in net earnings of Kindred at Home	0	0
Segment earnings	465	267
Operating Segments | Retail | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	10,709	8,970
Operating Segments | Retail | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,632	1,524
Operating Segments | Retail | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	809	896
Operating Segments | Retail | Total Medicare
Segment Reporting Information [Line Items]
Premiums	13,150	11,390
Operating Segments | Retail | Fully-insured
Segment Reporting Information [Line Items]
Premiums	140	125
Operating Segments | Retail | Specialty
Segment Reporting Information [Line Items]
Premiums	0	0
Operating Segments | Retail | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	677	553
Operating Segments | Retail | Total external revenues
Segment Reporting Information [Line Items]
Total revenues	13,972	12,070
Operating Segments | Retail | Services
Segment Reporting Information [Line Items]
Services revenue	5	2
Operating Segments | Retail | Services | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0
Operating Segments | Retail | Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue	5	2
Operating Segments | Retail | Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0
Operating Segments | Group and Specialty
Segment Reporting Information [Line Items]
Premiums	1,684	1,739
Investment income	5	7
Total revenues	1,887	1,970
Benefits	1,287	1,273
Operating costs	413	463
Depreciation and amortization	22	23
Total operating expenses	1,722	1,759
Income from operations	165	211
Interest expense	0	0
Other expense, net	0
Income before income taxes and equity in net earnings	165	211
Equity in net earnings of Kindred at Home	0	0
Segment earnings	165	211
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	1,311	1,392
Operating Segments | Group and Specialty | Specialty
Segment Reporting Information [Line Items]
Premiums	373	347
Operating Segments | Group and Specialty | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	0	0
Operating Segments | Group and Specialty | Total external revenues
Segment Reporting Information [Line Items]
Total revenues	1,878	1,958
Operating Segments | Group and Specialty | Services
Segment Reporting Information [Line Items]
Services revenue	194	219
Operating Segments | Group and Specialty | Services | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0
Operating Segments | Group and Specialty | Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue	194	219
Operating Segments | Group and Specialty | Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0
Operating Segments | Healthcare Services
Segment Reporting Information [Line Items]
Premiums	0	0
Investment income	0	6
Total revenues	6,098	5,663
Benefits	0	0
Operating costs	5,888	5,441
Depreciation and amortization	38	49
Total operating expenses	5,926	5,490
Income from operations	172	173
Interest expense	0	0
Other expense, net	0
Income before income taxes and equity in net earnings	172	173
Equity in net earnings of Kindred at Home	3	0
Segment earnings	175	173
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 | Total external revenues
Segment Reporting Information [Line Items]
Total revenues	156	104
Operating Segments | Healthcare Services | Services
Segment Reporting Information [Line Items]
Services revenue	156	104
Operating Segments | Healthcare Services | Services | Provider
Segment Reporting Information [Line Items]
Services revenue	120	65
Operating Segments | Healthcare Services | Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue	0	0
Operating Segments | Healthcare Services | Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	36	39
Operating Segments | Individual Commercial
Segment Reporting Information [Line Items]
Premiums		(5)
Investment income		0
Total revenues		(5)
Benefits		(60)
Operating costs		2
Depreciation and amortization		0
Total operating expenses		(58)
Income from operations		53
Interest expense		0
Income before income taxes and equity in net earnings		53
Equity in net earnings of Kindred at Home		0
Segment earnings		53
Operating Segments | Individual Commercial | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums		0
Operating Segments | Individual Commercial | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums		0
Operating Segments | Individual Commercial | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums		0
Operating Segments | Individual Commercial | Total Medicare
Segment Reporting Information [Line Items]
Premiums		0
Operating Segments | Individual Commercial | Fully-insured
Segment Reporting Information [Line Items]
Premiums		(5)
Operating Segments | Individual Commercial | Specialty
Segment Reporting Information [Line Items]
Premiums		0
Operating Segments | Individual Commercial | Medicaid and other
Segment Reporting Information [Line Items]
Premiums		0
Operating Segments | Individual Commercial | Total external revenues
Segment Reporting Information [Line Items]
Total revenues		(5)
Operating Segments | Individual Commercial | Services
Segment Reporting Information [Line Items]
Services revenue		0
Operating Segments | Individual Commercial | Services | Provider
Segment Reporting Information [Line Items]
Services revenue		0
Operating Segments | Individual Commercial | Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue		0
Operating Segments | Individual Commercial | Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue		0
Intersegment revenues
Segment Reporting Information [Line Items]
Total revenues	(5,946)	(5,558)
Intersegment revenues | Services
Segment Reporting Information [Line Items]
Total revenues	(4,310)	(4,023)
Intersegment revenues | Products
Segment Reporting Information [Line Items]
Total revenues	(1,636)	(1,535)
Intersegment revenues | Retail
Segment Reporting Information [Line Items]
Total revenues	0	0
Intersegment revenues | Retail | Services
Segment Reporting Information [Line Items]
Total revenues	0	0
Intersegment revenues | Retail | Products
Segment Reporting Information [Line Items]
Total revenues	0	0
Intersegment revenues | Group and Specialty
Segment Reporting Information [Line Items]
Total revenues	4	5
Intersegment revenues | Group and Specialty | Services
Segment Reporting Information [Line Items]
Total revenues	4	5
Intersegment revenues | Group and Specialty | Products
Segment Reporting Information [Line Items]
Total revenues	0	0
Intersegment revenues | Healthcare Services
Segment Reporting Information [Line Items]
Total revenues	5,942	5,553
Intersegment revenues | Healthcare Services | Services
Segment Reporting Information [Line Items]
Total revenues	4,306	4,018
Intersegment revenues | Healthcare Services | Products
Segment Reporting Information [Line Items]
Total revenues	1,636	1,535
Intersegment revenues | Individual Commercial
Segment Reporting Information [Line Items]
Total revenues		0
Intersegment revenues | Individual Commercial | Services
Segment Reporting Information [Line Items]
Total revenues		0
Intersegment revenues | Individual Commercial | Products
Segment Reporting Information [Line Items]
Total revenues		0
Other Businesses
Segment Reporting Information [Line Items]
Premiums		9
Investment income		35
Total revenues		46
Benefits		26
Operating costs		2
Depreciation and amortization		0
Total operating expenses		28
Income from operations		18
Interest expense		0
Income before income taxes and equity in net earnings		18
Equity in net earnings of Kindred at Home		0
Segment earnings		18
Other Businesses | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums		0
Other Businesses | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums		0
Other Businesses | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums		0
Other Businesses | Total Medicare
Segment Reporting Information [Line Items]
Premiums		0
Other Businesses | Fully-insured
Segment Reporting Information [Line Items]
Premiums		0
Other Businesses | Specialty
Segment Reporting Information [Line Items]
Premiums		0
Other Businesses | Medicaid and other
Segment Reporting Information [Line Items]
Premiums		9
Other Businesses | Total external revenues
Segment Reporting Information [Line Items]
Total revenues		11
Other Businesses | Services
Segment Reporting Information [Line Items]
Services revenue		2
Other Businesses | Services | Provider
Segment Reporting Information [Line Items]
Services revenue		0
Other Businesses | Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue		2
Other Businesses | Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue		0
Eliminations/ Corporate
Segment Reporting Information [Line Items]
Premiums	0	0
Investment income	55	56
Total revenues	(5,891)	(5,502)
Benefits	(121)	(121)
Operating costs	(5,789)	(5,381)
Depreciation and amortization	(26)	(38)
Total operating expenses	(5,936)	(5,540)
Income from operations	45	38
Interest expense	62	53
Other expense, net	39
Income before income taxes and equity in net earnings	(56)	(15)
Equity in net earnings of Kindred at Home	0	0
Segment earnings	(56)	(15)
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 | Total external revenues
Segment Reporting Information [Line Items]
Total revenues	0	0
Eliminations/ Corporate | Services
Segment Reporting Information [Line Items]
Services revenue	0	0
Eliminations/ Corporate | Services | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0
Eliminations/ Corporate | Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue	0	0
Eliminations/ Corporate | Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	$ 0	$ 0