SEGMENT INFORMATION - Segment Results (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Premiums	$ 15,712	$ 13,712	$ 47,139	$ 41,236
Services revenue	393	381	1,103	1,090
Total external revenues	16,105	14,093	48,242	42,326
Intersegment revenues	0	0	0	0
Investment income	136	113	351	418
Total revenues	16,241	14,206	48,593	42,744
Benefits	13,357	11,243	40,168	34,449
Operating costs	1,889	1,900	5,252	5,410
Depreciation and amortization	127	102	343	302
Total operating expenses	15,373	13,245	45,763	40,161
Income from operations	868	961	2,830	2,583
(Gain) loss on sale of business	0	(4)	0	786
Interest expense	62	53	184	159
Other (income) expense, net	(82)	11	(217)	11
Income before income taxes and equity in net earnings	888	901	2,863	1,627
Equity in net earnings of Kindred at Home	1	9	16	9
Segment earnings	889	910	2,879	1,636
Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	10,752	8,912	32,254	26,790
Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,609	1,542	4,867	4,575
Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	781	893	2,408	2,703
Total Medicare
Segment Reporting Information [Line Items]
Premiums	13,142	11,347	39,529	34,068
Fully-insured
Segment Reporting Information [Line Items]
Premiums	1,428	1,475	4,307	4,468
Specialty
Segment Reporting Information [Line Items]
Premiums	400	325	1,160	1,014
Medicaid and other
Segment Reporting Information [Line Items]
Premiums	742	565	2,143	1,686
Provider
Segment Reporting Information [Line Items]
Services revenue	136	113	367	290
ASO and other
Segment Reporting Information [Line Items]
Services revenue	204	216	601	652
Pharmacy
Segment Reporting Information [Line Items]
Services revenue	53	52	135	148
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	14,034	12,037	42,106	36,111
Services revenue	4	1	14	6
Total external revenues	14,038	12,038	42,120	36,117
Intersegment revenues	0	0	0	0
Investment income	50	35	139	102
Total revenues	14,088	12,073	42,259	36,219
Benefits	12,050	10,020	36,396	30,842
Operating costs	1,310	1,352	3,664	3,784
Depreciation and amortization	89	67	239	199
Total operating expenses	13,449	11,439	40,299	34,825
Income from operations	639	634	1,960	1,394
(Gain) loss on sale of business		0		0
Interest expense	0	0	0	0
Other (income) expense, net	0	0	0	0
Income before income taxes and equity in net earnings	639	634	1,960	1,394
Equity in net earnings of Kindred at Home	0	0	0	0
Segment earnings	639	634	1,960	1,394
Operating Segments | Retail | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	10,752	8,912	32,254	26,790
Operating Segments | Retail | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,609	1,542	4,867	4,575
Operating Segments | Retail | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	781	893	2,408	2,703
Operating Segments | Retail | Total Medicare
Segment Reporting Information [Line Items]
Premiums	13,142	11,347	39,529	34,068
Operating Segments | Retail | Fully-insured
Segment Reporting Information [Line Items]
Premiums	150	129	434	379
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	742	561	2,143	1,664
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	1	14	6
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	1,678	1,670	5,033	5,097
Services revenue	200	215	587	642
Total external revenues	1,878	1,885	5,620	5,739
Intersegment revenues	4	4	13	13
Investment income	7	5	17	18
Total revenues	1,889	1,894	5,650	5,770
Benefits	1,448	1,347	4,177	3,977
Operating costs	413	445	1,232	1,355
Depreciation and amortization	24	21	67	66
Total operating expenses	1,885	1,813	5,476	5,398
Income from operations	4	81	174	372
(Gain) loss on sale of business		0		0
Interest expense	0	0	0	0
Other (income) expense, net	0	0	0	0
Income before income taxes and equity in net earnings	4	81	174	372
Equity in net earnings of Kindred at Home	0	0	0	0
Segment earnings	4	81	174	372
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	1,278	1,345	3,873	4,083
Operating Segments | Group and Specialty | Specialty
Segment Reporting Information [Line Items]
Premiums	400	325	1,160	1,014
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	200	215	587	642
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	4	4	13	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	189	165	502	438
Total external revenues	189	165	502	438
Intersegment revenues	6,413	5,790	18,584	17,148
Investment income	0	11	1	34
Total revenues	6,602	5,966	19,087	17,620
Benefits	0	0	0	0
Operating costs	6,348	5,720	18,371	16,910
Depreciation and amortization	43	40	121	125
Total operating expenses	6,391	5,760	18,492	17,035
Income from operations	211	206	595	585
(Gain) loss on sale of business		0		0
Interest expense	0	0	0	0
Other (income) expense, net	0	0	0	0
Income before income taxes and equity in net earnings	211	206	595	585
Equity in net earnings of Kindred at Home	1	9	16	9
Segment earnings	212	215	611	594
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	136	113	367	290
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	53	52	135	148
Operating Segments | Healthcare Services | Services
Segment Reporting Information [Line Items]
Intersegment revenues	4,654	4,214	13,456	12,426
Operating Segments | Healthcare Services | Products
Segment Reporting Information [Line Items]
Intersegment revenues	1,759	1,576	5,128	4,722
Operating Segments | Individual Commercial
Segment Reporting Information [Line Items]
Premiums		1		6
Services revenue		0		0
Total external revenues		1		6
Intersegment revenues		0		0
Investment income		0		0
Total revenues		1		6
Benefits		(4)		(73)
Operating costs		0		3
Depreciation and amortization		0		0
Total operating expenses		(4)		(70)
Income from operations		5		76
(Gain) loss on sale of business		0		0
Interest expense		0		0
Other (income) expense, net		0		0
Income before income taxes and equity in net earnings		5		76
Equity in net earnings of Kindred at Home		0		0
Segment earnings		5		76
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		1		6
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		4		22
Services revenue		0		4
Total external revenues		4		26
Intersegment revenues		0		0
Investment income		10		110
Total revenues		14		136
Benefits		12		77
Operating costs		2		6
Depreciation and amortization		0		0
Total operating expenses		14		83
Income from operations		0		53
(Gain) loss on sale of business		0		0
Interest expense		0		0
Other (income) expense, net		0		0
Income before income taxes and equity in net earnings		0		53
Equity in net earnings of Kindred at Home		0		0
Segment earnings		0		53
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		4		22
Other Businesses | Provider
Segment Reporting Information [Line Items]
Services revenue		0		0
Other Businesses | ASO and other
Segment Reporting Information [Line Items]
Services revenue		0		4
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	0
Services revenue	0	0	0	0
Total external revenues	0	0	0	0
Intersegment revenues	(6,417)	(5,794)	(18,597)	(17,161)
Investment income	79	52	194	154
Total revenues	(6,338)	(5,742)	(18,403)	(17,007)
Benefits	(141)	(132)	(405)	(374)
Operating costs	(6,182)	(5,619)	(18,015)	(16,648)
Depreciation and amortization	(29)	(26)	(84)	(88)
Total operating expenses	(6,352)	(5,777)	(18,504)	(17,110)
Income from operations	14	35	101	103
(Gain) loss on sale of business		(4)		786
Interest expense	62	53	184	159
Other (income) expense, net	(82)	11	(217)	11
Income before income taxes and equity in net earnings	34	(25)	134	(853)
Equity in net earnings of Kindred at Home	0	0	0	0
Segment earnings	34	(25)	134	(853)
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	(4,658)	(4,218)	(13,469)	(12,439)
Eliminations/ Corporate | Products
Segment Reporting Information [Line Items]
Intersegment revenues	$ (1,759)	$ (1,576)	$ (5,128)	$ (4,722)