SEGMENT INFORMATION - Segment Results (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Premiums									$ 62,948	$ 54,941	$ 52,380
Services revenue									1,439	1,457	982
Total external revenues									64,387	56,398	53,362
Intersegment revenues									0	0	0
Investment income									501	514	405
Total revenues	$ 16,295	$ 16,241	$ 16,245	$ 16,107	$ 14,168	$ 14,206	$ 14,259	$ 14,279	64,888	56,912	53,767
Benefits									53,857	45,882	43,496
Operating costs									7,381	7,525	6,567
Merger termination fee and related costs, net									0	0	(936)
Depreciation and amortization									458	405	378
Total operating expenses									61,696	53,812	49,505
Income from operations									3,192	3,100	4,262
Loss on sale of business									0	786	0
Interest expense									242	218	242
Other (income) expense, net									(506)	33	0
Income before income taxes and equity in net earnings	$ 593	$ 888	$ 1,229	$ 746	$ 436	$ 901	$ 19	$ 707	3,456	2,063	4,020
Equity in net earnings of Kindred at Home									14	11	0
Segment earnings									3,470	2,074	4,020
Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									43,128	35,656	32,720
Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									6,475	6,103	5,155
Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums									3,165	3,584	3,702
Total Medicare
Segment Reporting Information [Line Items]
Premiums									52,768	45,343	41,577
Fully-insured
Segment Reporting Information [Line Items]
Premiums									5,711	5,962	6,887
Specialty
Segment Reporting Information [Line Items]
Premiums									1,571	1,359	1,310
Medicaid and other
Segment Reporting Information [Line Items]
Premiums									2,898	2,277	2,606
Provider
Segment Reporting Information [Line Items]
Services revenue									446	404	258
ASO and other
Segment Reporting Information [Line Items]
Services revenue									807	850	644
Pharmacy
Segment Reporting Information [Line Items]
Services revenue									186	203	80
Services
Segment Reporting Information [Line Items]
Intersegment revenues									0	0	0
Products
Segment Reporting Information [Line Items]
Intersegment revenues									0	0	0
Operating Segments | Retail
Segment Reporting Information [Line Items]
Premiums									56,254	48,108	44,626
Services revenue									17	11	10
Total external revenues									56,271	48,119	44,636
Intersegment revenues									0	0	0
Investment income									195	136	90
Total revenues									56,466	48,255	44,726
Benefits									48,602	40,925	38,218
Operating costs									5,306	5,327	4,292
Merger termination fee and related costs, net											0
Depreciation and amortization									323	270	238
Total operating expenses									54,231	46,522	42,748
Income from operations									2,235	1,733	1,978
Loss on sale of business										0
Interest expense									0	0	0
Other (income) expense, net									0	0
Income before income taxes and equity in net earnings									2,235	1,733	1,978
Equity in net earnings of Kindred at Home									0	0	0
Segment earnings									2,235	1,733	1,978
Operating Segments | Retail | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									43,128	35,656	32,720
Operating Segments | Retail | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									6,475	6,103	5,155
Operating Segments | Retail | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums									3,165	3,584	3,702
Operating Segments | Retail | Total Medicare
Segment Reporting Information [Line Items]
Premiums									52,768	45,343	41,577
Operating Segments | Retail | Fully-insured
Segment Reporting Information [Line Items]
Premiums									588	510	478
Operating Segments | Retail | Specialty
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Retail | Medicaid and other
Segment Reporting Information [Line Items]
Premiums									2,898	2,255	2,571
Operating Segments | Retail | Provider
Segment Reporting Information [Line Items]
Services revenue									0	0	0
Operating Segments | Retail | ASO and other
Segment Reporting Information [Line Items]
Services revenue									17	11	10
Operating Segments | Retail | Pharmacy
Segment Reporting Information [Line Items]
Services revenue									0	0	0
Operating Segments | Retail | Services
Segment Reporting Information [Line Items]
Intersegment revenues									0	0	0
Operating Segments | Retail | Products
Segment Reporting Information [Line Items]
Intersegment revenues									0	0	0
Operating Segments | Group and Specialty
Segment Reporting Information [Line Items]
Premiums									6,694	6,803	6,772
Services revenue									790	835	626
Total external revenues									7,484	7,638	7,398
Intersegment revenues									18	18	20
Investment income									23	23	31
Total revenues									7,525	7,679	7,449
Benefits									5,758	5,420	5,363
Operating costs									1,651	1,810	1,590
Merger termination fee and related costs, net											0
Depreciation and amortization									88	88	84
Total operating expenses									7,497	7,318	7,037
Income from operations									28	361	412
Loss on sale of business										0
Interest expense									0	0	0
Other (income) expense, net									0	0
Income before income taxes and equity in net earnings									28	361	412
Equity in net earnings of Kindred at Home									0	0	0
Segment earnings									28	361	412
Operating Segments | Group and Specialty | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Group and Specialty | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Group and Specialty | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Group and Specialty | Total Medicare
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Group and Specialty | Fully-insured
Segment Reporting Information [Line Items]
Premiums									5,123	5,444	5,462
Operating Segments | Group and Specialty | Specialty
Segment Reporting Information [Line Items]
Premiums									1,571	1,359	1,310
Operating Segments | Group and Specialty | Medicaid and other
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Group and Specialty | Provider
Segment Reporting Information [Line Items]
Services revenue									0	0	0
Operating Segments | Group and Specialty | ASO and other
Segment Reporting Information [Line Items]
Services revenue									790	835	626
Operating Segments | Group and Specialty | Pharmacy
Segment Reporting Information [Line Items]
Services revenue									0	0	0
Operating Segments | Group and Specialty | Services
Segment Reporting Information [Line Items]
Intersegment revenues									18	18	20
Operating Segments | Group and Specialty | Products
Segment Reporting Information [Line Items]
Intersegment revenues									0	0	0
Operating Segments | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Services revenue									632	607	338
Total external revenues									632	607	338
Intersegment revenues									25,149	23,170	23,585
Investment income									2	34	35
Total revenues									25,783	23,811	23,958
Benefits									0	0	0
Operating costs									24,852	22,905	22,848
Merger termination fee and related costs, net											0
Depreciation and amortization									156	163	143
Total operating expenses									25,008	23,068	22,991
Income from operations									775	743	967
Loss on sale of business										0
Interest expense									0	0	0
Other (income) expense, net									0	0
Income before income taxes and equity in net earnings									775	743	967
Equity in net earnings of Kindred at Home									14	11	0
Segment earnings									789	754	967
Operating Segments | Healthcare Services | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Healthcare Services | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Healthcare Services | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Healthcare Services | Total Medicare
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Healthcare Services | Fully-insured
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Healthcare Services | Specialty
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Healthcare Services | Medicaid and other
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Healthcare Services | Provider
Segment Reporting Information [Line Items]
Services revenue									446	404	258
Operating Segments | Healthcare Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue									0	0	0
Operating Segments | Healthcare Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue									186	203	80
Operating Segments | Healthcare Services | Services
Segment Reporting Information [Line Items]
Intersegment revenues									18,255	16,840	17,293
Operating Segments | Healthcare Services | Products
Segment Reporting Information [Line Items]
Intersegment revenues									6,894	6,330	6,292
Operating Segments | Individual Commercial
Segment Reporting Information [Line Items]
Premiums										8	947
Services revenue										0	0
Total external revenues										8	947
Intersegment revenues										0	0
Investment income										0	4
Total revenues										8	951
Benefits										(70)	544
Operating costs										4	201
Merger termination fee and related costs, net											0
Depreciation and amortization										0	13
Total operating expenses										(66)	758
Income from operations										74	193
Loss on sale of business										0
Interest expense										0	0
Other (income) expense, net										0
Income before income taxes and equity in net earnings										74	193
Equity in net earnings of Kindred at Home										0	0
Segment earnings										74	193
Operating Segments | Individual Commercial | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums										0	0
Operating Segments | Individual Commercial | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums										0	0
Operating Segments | Individual Commercial | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums										0	0
Operating Segments | Individual Commercial | Total Medicare
Segment Reporting Information [Line Items]
Premiums										0	0
Operating Segments | Individual Commercial | Fully-insured
Segment Reporting Information [Line Items]
Premiums										8	947
Operating Segments | Individual Commercial | Specialty
Segment Reporting Information [Line Items]
Premiums										0	0
Operating Segments | Individual Commercial | Medicaid and other
Segment Reporting Information [Line Items]
Premiums										0	0
Operating Segments | Individual Commercial | Provider
Segment Reporting Information [Line Items]
Services revenue										0	0
Operating Segments | Individual Commercial | ASO and other
Segment Reporting Information [Line Items]
Services revenue										0	0
Operating Segments | Individual Commercial | Pharmacy
Segment Reporting Information [Line Items]
Services revenue										0	0
Operating Segments | Individual Commercial | Services
Segment Reporting Information [Line Items]
Intersegment revenues										0	0
Operating Segments | Individual Commercial | Products
Segment Reporting Information [Line Items]
Intersegment revenues										0	0
Other Businesses
Segment Reporting Information [Line Items]
Premiums										22	35
Services revenue										4	8
Total external revenues										26	43
Intersegment revenues										0	0
Investment income										110	87
Total revenues										136	130
Benefits										77	131
Operating costs										6	12
Merger termination fee and related costs, net											0
Depreciation and amortization										0	0
Total operating expenses										83	143
Income from operations										53	(13)
Loss on sale of business										0
Interest expense										0	0
Other (income) expense, net										0
Income before income taxes and equity in net earnings										53	(13)
Equity in net earnings of Kindred at Home										0	0
Segment earnings										53	(13)
Other Businesses | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums										0	0
Other Businesses | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums										0	0
Other Businesses | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums										0	0
Other Businesses | Total Medicare
Segment Reporting Information [Line Items]
Premiums										0	0
Other Businesses | Fully-insured
Segment Reporting Information [Line Items]
Premiums										0	0
Other Businesses | Specialty
Segment Reporting Information [Line Items]
Premiums										0	0
Other Businesses | Medicaid and other
Segment Reporting Information [Line Items]
Premiums										22	35
Other Businesses | Provider
Segment Reporting Information [Line Items]
Services revenue										0	0
Other Businesses | ASO and other
Segment Reporting Information [Line Items]
Services revenue										4	8
Other Businesses | Pharmacy
Segment Reporting Information [Line Items]
Services revenue										0	0
Other Businesses | Services
Segment Reporting Information [Line Items]
Intersegment revenues										0	0
Other Businesses | Products
Segment Reporting Information [Line Items]
Intersegment revenues										0	0
Eliminations/Corporate
Segment Reporting Information [Line Items]
Premiums									0	0	0
Services revenue									0	0	0
Total external revenues									0	0	0
Intersegment revenues									(25,167)	(23,188)	(23,605)
Investment income									281	211	158
Total revenues									(24,886)	(22,977)	(23,447)
Benefits									(503)	(470)	(760)
Operating costs									(24,428)	(22,527)	(22,376)
Merger termination fee and related costs, net											(936)
Depreciation and amortization									(109)	(116)	(100)
Total operating expenses									(25,040)	(23,113)	(24,172)
Income from operations									154	136	725
Loss on sale of business										786
Interest expense									242	218	242
Other (income) expense, net									(506)	33
Income before income taxes and equity in net earnings									418	(901)	483
Equity in net earnings of Kindred at Home									0	0	0
Segment earnings									418	(901)	483
Eliminations/Corporate | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									0	0	0
Eliminations/Corporate | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									0	0	0
Eliminations/Corporate | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums									0	0	0
Eliminations/Corporate | Total Medicare
Segment Reporting Information [Line Items]
Premiums									0	0	0
Eliminations/Corporate | Fully-insured
Segment Reporting Information [Line Items]
Premiums									0	0	0
Eliminations/Corporate | Specialty
Segment Reporting Information [Line Items]
Premiums									0	0	0
Eliminations/Corporate | Medicaid and other
Segment Reporting Information [Line Items]
Premiums									0	0	0
Eliminations/Corporate | Provider
Segment Reporting Information [Line Items]
Services revenue									0	0	0
Eliminations/Corporate | ASO and other
Segment Reporting Information [Line Items]
Services revenue									0	0	0
Eliminations/Corporate | Pharmacy
Segment Reporting Information [Line Items]
Services revenue									0	0	0
Eliminations/Corporate | Services
Segment Reporting Information [Line Items]
Intersegment revenues									(18,273)	(16,858)	(17,313)
Eliminations/Corporate | Products
Segment Reporting Information [Line Items]
Intersegment revenues									$ (6,894)	$ (6,330)	$ (6,292)