SEGMENT INFORMATION - Segment Results (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Premiums	$ 15,776	$ 13,713	$ 31,427	$ 27,524
Services revenue	355	382	710	709
Total external revenues	16,131	14,095	32,137	28,233
Intersegment revenues	0	0	0	0
Investment income	114	164	215	305
Total revenues	16,245	14,259	32,352	28,538
Benefits	13,318	11,536	26,811	23,206
Operating costs	1,703	1,761	3,363	3,510
Depreciation and amortization	109	100	216	200
Total operating expenses	15,130	13,397	30,390	26,916
Income from operations	1,115	862	1,962	1,622
Loss on sale of business	0	790	0	790
Interest expense	60	53	122	106
Other income, net	(174)	0	(135)	0
Income before income taxes and equity in net earnings	1,229	19	1,975	726
Equity in net earnings of Kindred at Home	12	0	15	0
Segment earnings	1,241	19	1,990	726
Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	10,793	8,908	21,502	17,878
Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,626	1,509	3,258	3,033
Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	818	914	1,627	1,810
Total Medicare
Segment Reporting Information [Line Items]
Premiums	13,237	11,331	26,387	22,721
Fully-insured
Segment Reporting Information [Line Items]
Premiums	1,428	1,481	2,879	2,993
Specialty
Segment Reporting Information [Line Items]
Premiums	387	342	760	689
Medicaid and other
Segment Reporting Information [Line Items]
Premiums	724	559	1,401	1,121
Provider
Segment Reporting Information [Line Items]
Services revenue	111	112	231	177
ASO and other
Segment Reporting Information [Line Items]
Services revenue	198	213	397	436
Pharmacy
Segment Reporting Information [Line Items]
Services revenue	46	57	82	96
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	14,105	12,006	28,072	24,074
Services revenue	5	3	10	5
Total external revenues	14,110	12,009	28,082	24,079
Intersegment revenues	0	0	0	0
Investment income	48	30	89	67
Total revenues	14,158	12,039	28,171	24,146
Benefits	12,019	10,270	24,346	20,822
Operating costs	1,206	1,210	2,354	2,432
Depreciation and amortization	77	66	150	132
Total operating expenses	13,302	11,546	26,850	23,386
Income from operations	856	493	1,321	760
Loss on sale of business		0		0
Interest expense	0	0	0	0
Other income, net	0		0
Income before income taxes and equity in net earnings	856	493	1,321	760
Equity in net earnings of Kindred at Home	0	0	0	0
Segment earnings	856	493	1,321	760
Operating Segments | Retail | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	10,793	8,908	21,502	17,878
Operating Segments | Retail | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,626	1,509	3,258	3,033
Operating Segments | Retail | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	818	914	1,627	1,810
Operating Segments | Retail | Total Medicare
Segment Reporting Information [Line Items]
Premiums	13,237	11,331	26,387	22,721
Operating Segments | Retail | Fully-insured
Segment Reporting Information [Line Items]
Premiums	144	125	284	250
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	724	550	1,401	1,103
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	5	3	10	5
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	1,671	1,688	3,355	3,427
Services revenue	193	208	387	427
Total external revenues	1,864	1,896	3,742	3,854
Intersegment revenues	5	4	9	9
Investment income	5	6	10	13
Total revenues	1,874	1,906	3,761	3,876
Benefits	1,442	1,357	2,729	2,630
Operating costs	406	447	819	910
Depreciation and amortization	21	22	43	45
Total operating expenses	1,869	1,826	3,591	3,585
Income from operations	5	80	170	291
Loss on sale of business		0		0
Interest expense	0	0	0	0
Other income, net	0		0
Income before income taxes and equity in net earnings	5	80	170	291
Equity in net earnings of Kindred at Home	0	0	0	0
Segment earnings	5	80	170	291
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	1,284	1,346	2,595	2,738
Operating Segments | Group and Specialty | Specialty
Segment Reporting Information [Line Items]
Premiums	387	342	760	689
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	193	208	387	427
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	5	4	9	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	157	169	313	273
Total external revenues	157	169	313	273
Intersegment revenues	6,229	5,805	12,171	11,358
Investment income	1	17	1	23
Total revenues	6,387	5,991	12,485	11,654
Benefits	0	0	0	0
Operating costs	6,135	5,749	12,023	11,190
Depreciation and amortization	40	36	78	85
Total operating expenses	6,175	5,785	12,101	11,275
Income from operations	212	206	384	379
Loss on sale of business		0		0
Interest expense	0	0	0	0
Other income, net	0		0
Income before income taxes and equity in net earnings	212	206	384	379
Equity in net earnings of Kindred at Home	12	0	15	0
Segment earnings	224	206	399	379
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	111	112	231	177
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	46	57	82	96
Operating Segments | Healthcare Services | Services
Segment Reporting Information [Line Items]
Intersegment revenues	4,496	4,194	8,802	8,212
Operating Segments | Healthcare Services | Products
Segment Reporting Information [Line Items]
Intersegment revenues	1,733	1,611	3,369	3,146
Operating Segments | Individual Commercial
Segment Reporting Information [Line Items]
Premiums		10		5
Services revenue		0		0
Total external revenues		10		5
Intersegment revenues		0		0
Investment income		0		0
Total revenues		10		5
Benefits		(9)		(69)
Operating costs		1		3
Depreciation and amortization		0		0
Total operating expenses		(8)		(66)
Income from operations		18		71
Loss on sale of business		0		0
Interest expense		0		0
Income before income taxes and equity in net earnings		18		71
Equity in net earnings of Kindred at Home		0		0
Segment earnings		18		71
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		10		5
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		9		18
Services revenue		2		4
Total external revenues		11		22
Intersegment revenues		0		0
Investment income		65		100
Total revenues		76		122
Benefits		39		65
Operating costs		2		4
Depreciation and amortization		0		0
Total operating expenses		41		69
Income from operations		35		53
Loss on sale of business		0		0
Interest expense		0		0
Income before income taxes and equity in net earnings		35		53
Equity in net earnings of Kindred at Home		0		0
Segment earnings		35		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		9		18
Other Businesses | Provider
Segment Reporting Information [Line Items]
Services revenue		0		0
Other Businesses | ASO and other
Segment Reporting Information [Line Items]
Services revenue		2		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	(6,234)	(5,809)	(12,180)	(11,367)
Investment income	60	46	115	102
Total revenues	(6,174)	(5,763)	(12,065)	(11,265)
Benefits	(143)	(121)	(264)	(242)
Operating costs	(6,044)	(5,648)	(11,833)	(11,029)
Depreciation and amortization	(29)	(24)	(55)	(62)
Total operating expenses	(6,216)	(5,793)	(12,152)	(11,333)
Income from operations	42	30	87	68
Loss on sale of business		790		790
Interest expense	60	53	122	106
Other income, net	(174)		(135)
Income before income taxes and equity in net earnings	156	(813)	100	(828)
Equity in net earnings of Kindred at Home	0	0	0	0
Segment earnings	156	(813)	100	(828)
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	(4,501)	(4,198)	(8,811)	(8,221)
Eliminations/ Corporate | Products
Segment Reporting Information [Line Items]
Intersegment revenues	$ (1,733)	$ (1,611)	$ (3,369)	$ (3,146)