SEGMENT INFORMATION - Reconciliation (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Premiums	$ 13,712	$ 12,955	$ 41,236	$ 39,556
Services revenue	381	223	1,090	706
Investment income	113	104	418	316
Total revenues	14,206	13,282	42,744	40,578
Benefits	11,243	10,642	34,449	32,857
Operating costs	1,900	1,688	5,410	4,694
Merger termination fee and related costs, net	0	0	0	(947)
Depreciation and amortization	102	94	302	278
Total operating expenses	13,245	12,424	40,161	36,882
Income (loss) from operations	961	858	2,583	3,696
Loss on sale of business	(4)	0	786	0
Interest expense	53	59	159	166
Other expense, net	11	0	11	0
Income (loss) before income taxes and equity in net earnings	901	799	1,627	3,530
Equity in net earnings of Kindred at Home	9	0	9	0
Segment earnings	910	799	1,636	3,530
Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	8,912	8,077	26,790	24,735
Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,542	1,272	4,575	3,867
Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	893	921	2,703	2,787
Total Medicare
Segment Reporting Information [Line Items]
Premiums	11,347	10,270	34,068	31,389
Fully-insured
Segment Reporting Information [Line Items]
Premiums	1,475	1,715	4,468	5,209
Specialty
Segment Reporting Information [Line Items]
Premiums	325	331	1,014	976
Medicaid and other
Segment Reporting Information [Line Items]
Premiums	565	639	1,686	1,982
Total external revenues
Segment Reporting Information [Line Items]
Total revenues	14,093	13,178	42,326	40,262
Services
Segment Reporting Information [Line Items]
Services revenue	381	223	1,090	706
Services | Provider
Segment Reporting Information [Line Items]
Services revenue	113	60	290	193
Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue	216	143	652	455
Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	52	20	148	58
Operating Segments | Retail
Segment Reporting Information [Line Items]
Premiums	12,037	11,021	36,111	33,700
Investment income	35	23	102	72
Total revenues	12,073	11,046	36,219	33,778
Benefits	10,020	9,294	30,842	29,017
Operating costs	1,352	1,081	3,784	2,998
Merger termination fee and related costs, net				0
Depreciation and amortization	67	61	199	176
Total operating expenses	11,439	10,436	34,825	32,191
Income (loss) from operations	634	610	1,394	1,587
Loss on sale of business	0		0
Interest expense	0	0	0	0
Other expense, net	0		0
Income (loss) before income taxes and equity in net earnings	634	610	1,394	1,587
Equity in net earnings of Kindred at Home	0	0	0	0
Segment earnings	634	610	1,394	1,587
Operating Segments | Retail | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	8,912	8,077	26,790	24,735
Operating Segments | Retail | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	1,542	1,272	4,575	3,867
Operating Segments | Retail | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	893	921	2,703	2,787
Operating Segments | Retail | Total Medicare
Segment Reporting Information [Line Items]
Premiums	11,347	10,270	34,068	31,389
Operating Segments | Retail | Fully-insured
Segment Reporting Information [Line Items]
Premiums	129	121	379	357
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	561	630	1,664	1,954
Operating Segments | Retail | Total external revenues
Segment Reporting Information [Line Items]
Total revenues	12,038	11,023	36,117	33,706
Operating Segments | Retail | Services
Segment Reporting Information [Line Items]
Services revenue	1	2	6	6
Operating Segments | Retail | Services | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Operating Segments | Retail | Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue	1	2	6	6
Operating Segments | Retail | Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Operating Segments | Group and Specialty
Segment Reporting Information [Line Items]
Premiums	1,670	1,701	5,097	5,074
Investment income	5	7	18	25
Total revenues	1,894	1,853	5,770	5,558
Benefits	1,347	1,354	3,977	3,952
Operating costs	445	385	1,355	1,178
Merger termination fee and related costs, net				0
Depreciation and amortization	21	21	66	63
Total operating expenses	1,813	1,760	5,398	5,193
Income (loss) from operations	81	93	372	365
Loss on sale of business	0		0
Interest expense	0	0	0	0
Other expense, net	0		0
Income (loss) before income taxes and equity in net earnings	81	93	372	365
Equity in net earnings of Kindred at Home	0	0	0	0
Segment earnings	81	93	372	365
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	1,345	1,370	4,083	4,098
Operating Segments | Group and Specialty | Specialty
Segment Reporting Information [Line Items]
Premiums	325	331	1,014	976
Operating Segments | Group and Specialty | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Group and Specialty | Total external revenues
Segment Reporting Information [Line Items]
Total revenues	1,885	1,841	5,739	5,518
Operating Segments | Group and Specialty | Services
Segment Reporting Information [Line Items]
Services revenue	215	140	642	444
Operating Segments | Group and Specialty | Services | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Operating Segments | Group and Specialty | Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue	215	140	642	444
Operating Segments | Group and Specialty | Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Operating Segments | Healthcare Services
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Investment income	11	9	34	25
Total revenues	5,966	6,000	17,620	17,940
Benefits	0	0	0	0
Operating costs	5,720	5,726	16,910	17,083
Merger termination fee and related costs, net				0
Depreciation and amortization	40	34	125	103
Total operating expenses	5,760	5,760	17,035	17,186
Income (loss) from operations	206	240	585	754
Loss on sale of business	0		0
Interest expense	0	0	0	0
Other expense, net	0		0
Income (loss) before income taxes and equity in net earnings	206	240	585	754
Equity in net earnings of Kindred at Home	9	0	9	0
Segment earnings	215	240	594	754
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 | Total external revenues
Segment Reporting Information [Line Items]
Total revenues	165	80	438	251
Operating Segments | Healthcare Services | Services
Segment Reporting Information [Line Items]
Services revenue	165	80	438	251
Operating Segments | Healthcare Services | Services | Provider
Segment Reporting Information [Line Items]
Services revenue	113	60	290	193
Operating Segments | Healthcare Services | Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Operating Segments | Healthcare Services | Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	52	20	148	58
Operating Segments | Individual Commercial
Segment Reporting Information [Line Items]
Premiums	1	224	6	754
Investment income	0	1	0	3
Total revenues	1	225	6	757
Benefits	(4)	147	(73)	389
Operating costs	0	49	3	151
Merger termination fee and related costs, net				0
Depreciation and amortization	0	3	0	10
Total operating expenses	(4)	199	(70)	550
Income (loss) from operations	5	26	76	207
Loss on sale of business	0		0
Interest expense	0	0	0	0
Other expense, net	0		0
Income (loss) before income taxes and equity in net earnings	5	26	76	207
Equity in net earnings of Kindred at Home	0	0	0	0
Segment earnings	5	26	76	207
Operating Segments | Individual Commercial | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Individual Commercial | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Individual Commercial | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Individual Commercial | Total Medicare
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Individual Commercial | Fully-insured
Segment Reporting Information [Line Items]
Premiums	1	224	6	754
Operating Segments | Individual Commercial | Specialty
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Individual Commercial | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Individual Commercial | Total external revenues
Segment Reporting Information [Line Items]
Total revenues	1	224	6	754
Operating Segments | Individual Commercial | Services
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Operating Segments | Individual Commercial | Services | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Operating Segments | Individual Commercial | Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Operating Segments | Individual Commercial | Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Intersegment revenues
Segment Reporting Information [Line Items]
Total revenues	(5,794)	(5,916)	(17,161)	(17,679)
Intersegment revenues | Services
Segment Reporting Information [Line Items]
Total revenues	(4,218)	(4,344)	(12,439)	(12,973)
Intersegment revenues | Products
Segment Reporting Information [Line Items]
Total revenues	(1,576)	(1,572)	(4,722)	(4,706)
Intersegment revenues | Retail
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Intersegment revenues | Retail | Services
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Intersegment revenues | Retail | Products
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Intersegment revenues | Group and Specialty
Segment Reporting Information [Line Items]
Total revenues	4	5	13	15
Intersegment revenues | Group and Specialty | Services
Segment Reporting Information [Line Items]
Total revenues	4	5	13	15
Intersegment revenues | Group and Specialty | Products
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Intersegment revenues | Healthcare Services
Segment Reporting Information [Line Items]
Total revenues	5,790	5,911	17,148	17,664
Intersegment revenues | Healthcare Services | Services
Segment Reporting Information [Line Items]
Total revenues	4,214	4,339	12,426	12,958
Intersegment revenues | Healthcare Services | Products
Segment Reporting Information [Line Items]
Total revenues	1,576	1,572	4,722	4,706
Intersegment revenues | Individual Commercial
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Intersegment revenues | Individual Commercial | Services
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Intersegment revenues | Individual Commercial | Products
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Other Businesses
Segment Reporting Information [Line Items]
Premiums	4	9	22	28
Investment income	10	22	110	64
Total revenues	14	32	136	97
Benefits	12	34	77	95
Operating costs	2	3	6	9
Merger termination fee and related costs, net				0
Depreciation and amortization	0	0	0	0
Total operating expenses	14	37	83	104
Income (loss) from operations	0	(5)	53	(7)
Loss on sale of business	0		0
Interest expense	0	0	0	0
Other expense, net	0		0
Income (loss) before income taxes and equity in net earnings	0	(5)	53	(7)
Equity in net earnings of Kindred at Home	0	0	0	0
Segment earnings	0	(5)	53	(7)
Other Businesses | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Other Businesses | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Other Businesses | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Other Businesses | Total Medicare
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Other Businesses | Fully-insured
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Other Businesses | Specialty
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Other Businesses | Medicaid and other
Segment Reporting Information [Line Items]
Premiums	4	9	22	28
Other Businesses | Total external revenues
Segment Reporting Information [Line Items]
Total revenues	4	10	26	33
Other Businesses | Services
Segment Reporting Information [Line Items]
Services revenue	0	1	4	5
Other Businesses | Services | Provider
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Other Businesses | Services | ASO and other
Segment Reporting Information [Line Items]
Services revenue	0	1	4	5
Other Businesses | Services | Pharmacy
Segment Reporting Information [Line Items]
Services revenue	0	0	0	0
Eliminations/ Corporate
Segment Reporting Information [Line Items]
Premiums	0	0
Investment income	52	42	154	127
Total revenues	(5,742)	(5,874)	(17,007)	(17,552)
Benefits	(132)	(187)	(374)	(596)
Operating costs	(5,619)	(5,556)	(16,648)	(16,725)
Merger termination fee and related costs, net				(947)
Depreciation and amortization	(26)	(25)	(88)	(74)
Total operating expenses	(5,777)	(5,768)	(17,110)	(18,342)
Income (loss) from operations	35	(106)	103	790
Loss on sale of business	(4)		786
Interest expense	53	59	159	166
Other expense, net	11		11
Income (loss) before income taxes and equity in net earnings	(25)	(165)	(853)	624
Equity in net earnings of Kindred at Home	0	0	0	0
Segment earnings	(25)	(165)	$ (853)	$ 624
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