SEGMENT INFORMATION - Information by Segment (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Premiums									$ 54,941	$ 52,380	$ 53,021
Services									1,457	982	969
Investment income									514	405	389
Total revenues	$ 14,168	$ 14,206	$ 14,259	$ 14,279	$ 13,189	$ 13,282	$ 13,534	$ 13,762	56,912	53,767	54,379
Benefits									45,882	43,496	45,007
Operating costs									7,525	6,567	7,173
Merger termination fee and related costs, net									0	(936)	104
Depreciation and amortization									405	378	354
Total operating expenses									53,812	49,505	52,638
Income from operations									3,100	4,262	1,741
Loss on sale of business									786	0	0
Interest expense									218	242	189
Other expense, net									33	0	0
Income (loss) before income taxes and equity in net earnings	$ 436	$ 901	$ 19	$ 707	$ 490	$ 799	$ 1,042	$ 1,689	2,063	4,020	1,552
Equity in net earnings of Kindred at Home									11	0	0
Segment earnings (losses)									2,074	4,020	1,552
Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									35,656	32,720	31,863
Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									6,103	5,155	4,283
Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums									3,584	3,702	4,009
Total Medicare
Segment Reporting Information [Line Items]
Premiums									45,343	41,577	40,155
Fully-insured
Segment Reporting Information [Line Items]
Premiums									5,962	6,887	8,897
Specialty
Segment Reporting Information [Line Items]
Premiums									1,359	1,310	1,279
Medicaid and other
Segment Reporting Information [Line Items]
Premiums									2,277	2,606	2,690
Provider
Segment Reporting Information [Line Items]
Services									404	258	278
ASO and other
Segment Reporting Information [Line Items]
Services									850	644	660
Pharmacy
Segment Reporting Information [Line Items]
Services									203	80	31
External Customers
Segment Reporting Information [Line Items]
Total revenues									56,398	53,362	53,990
Operating Segments | Retail
Segment Reporting Information [Line Items]
Premiums									48,108	44,626	43,223
Services									11	10	6
Investment income									136	90	90
Total revenues									48,255	44,726	43,319
Benefits									40,925	38,218	36,783
Operating costs									5,327	4,292	4,650
Merger termination fee and related costs, net										0	0
Depreciation and amortization									270	238	196
Total operating expenses									46,522	42,748	41,629
Income from operations									1,733	1,978	1,690
Loss on sale of business									0		0
Interest expense									0	0	0
Other expense, net									0
Income (loss) before income taxes and equity in net earnings									1,733	1,978	1,690
Equity in net earnings of Kindred at Home									0	0	0
Segment earnings (losses)									1,733	1,978	1,690
Operating Segments | Group and Specialty
Segment Reporting Information [Line Items]
Premiums									6,803	6,772	6,696
Services									835	626	643
Investment income									23	31	25
Total revenues									7,679	7,449	7,386
Benefits									5,420	5,363	5,233
Operating costs									1,810	1,590	1,727
Merger termination fee and related costs, net										0	0
Depreciation and amortization									88	84	82
Total operating expenses									7,318	7,037	7,042
Income from operations									361	412	344
Loss on sale of business									0		0
Interest expense									0	0	0
Other expense, net									0
Income (loss) before income taxes and equity in net earnings									361	412	344
Equity in net earnings of Kindred at Home									0	0	0
Segment earnings (losses)									361	412	344
Operating Segments | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Services									607	338	310
Investment income									34	35	30
Total revenues									23,811	23,958	25,312
Benefits									0	0	0
Operating costs									22,905	22,848	24,073
Merger termination fee and related costs, net										0	0
Depreciation and amortization									163	143	143
Total operating expenses									23,068	22,991	24,216
Income from operations									743	967	1,096
Loss on sale of business									0		0
Interest expense									0	0	0
Other expense, net									0
Income (loss) before income taxes and equity in net earnings									743	967	1,096
Equity in net earnings of Kindred at Home									11	0	0
Segment earnings (losses)									754	967	1,096
Operating Segments | Individual Commercial
Segment Reporting Information [Line Items]
Premiums									8	947	3,064
Services									0	0	0
Investment income									0	4	5
Total revenues									8	951	3,069
Benefits									(70)	544	3,301
Operating costs									4	201	601
Merger termination fee and related costs, net										0	0
Depreciation and amortization									0	13	36
Total operating expenses									(66)	758	3,938
Income from operations									74	193	(869)
Loss on sale of business									0		0
Interest expense									0	0	0
Other expense, net									0
Income (loss) before income taxes and equity in net earnings									74	193	(869)
Equity in net earnings of Kindred at Home									0	0	0
Segment earnings (losses)									74	193	(869)
Operating Segments | Individual Medicare Advantage | Retail
Segment Reporting Information [Line Items]
Premiums									35,656	32,720	31,863
Operating Segments | Individual Medicare Advantage | Group and Specialty
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Individual Medicare Advantage | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Individual Medicare Advantage | Individual Commercial
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Group Medicare Advantage | Retail
Segment Reporting Information [Line Items]
Premiums									6,103	5,155	4,283
Operating Segments | Group Medicare Advantage | Group and Specialty
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Group Medicare Advantage | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Group Medicare Advantage | Individual Commercial
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Medicare stand-alone PDP | Retail
Segment Reporting Information [Line Items]
Premiums									3,584	3,702	4,009
Operating Segments | Medicare stand-alone PDP | Group and Specialty
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Medicare stand-alone PDP | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Medicare stand-alone PDP | Individual Commercial
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Total Medicare | Retail
Segment Reporting Information [Line Items]
Premiums									45,343	41,577	40,155
Operating Segments | Total Medicare | Group and Specialty
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Total Medicare | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Total Medicare | Individual Commercial
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Fully-insured | Retail
Segment Reporting Information [Line Items]
Premiums									510	478	428
Operating Segments | Fully-insured | Group and Specialty
Segment Reporting Information [Line Items]
Premiums									5,444	5,462	5,405
Operating Segments | Fully-insured | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Fully-insured | Individual Commercial
Segment Reporting Information [Line Items]
Premiums									8	947	3,064
Operating Segments | Specialty | Retail
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Specialty | Group and Specialty
Segment Reporting Information [Line Items]
Premiums									1,359	1,310	1,279
Operating Segments | Specialty | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Specialty | Individual Commercial
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Medicaid and other | Retail
Segment Reporting Information [Line Items]
Premiums									2,255	2,571	2,640
Operating Segments | Medicaid and other | Group and Specialty
Segment Reporting Information [Line Items]
Premiums									0	0	12
Operating Segments | Medicaid and other | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Medicaid and other | Individual Commercial
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Provider | Retail
Segment Reporting Information [Line Items]
Services									0	0	0
Operating Segments | Provider | Group and Specialty
Segment Reporting Information [Line Items]
Services									0	0	0
Operating Segments | Provider | Healthcare Services
Segment Reporting Information [Line Items]
Services									404	258	278
Operating Segments | Provider | Individual Commercial
Segment Reporting Information [Line Items]
Services									0	0	0
Operating Segments | ASO and other | Retail
Segment Reporting Information [Line Items]
Services									11	10	6
Operating Segments | ASO and other | Group and Specialty
Segment Reporting Information [Line Items]
Services									835	626	643
Operating Segments | ASO and other | Healthcare Services
Segment Reporting Information [Line Items]
Services									0	0	1
Operating Segments | ASO and other | Individual Commercial
Segment Reporting Information [Line Items]
Services									0	0	0
Operating Segments | Pharmacy | Retail
Segment Reporting Information [Line Items]
Services									0	0	0
Operating Segments | Pharmacy | Group and Specialty
Segment Reporting Information [Line Items]
Services									0	0	0
Operating Segments | Pharmacy | Healthcare Services
Segment Reporting Information [Line Items]
Services									203	80	31
Operating Segments | Pharmacy | Individual Commercial
Segment Reporting Information [Line Items]
Services									0	0	0
Operating Segments | External Customers | Retail
Segment Reporting Information [Line Items]
Total revenues									48,119	44,636	43,229
Operating Segments | External Customers | Group and Specialty
Segment Reporting Information [Line Items]
Total revenues									7,638	7,398	7,339
Operating Segments | External Customers | Healthcare Services
Segment Reporting Information [Line Items]
Total revenues									607	338	310
Operating Segments | External Customers | Individual Commercial
Segment Reporting Information [Line Items]
Total revenues									8	947	3,064
Other Businesses
Segment Reporting Information [Line Items]
Premiums									22	35	38
Services									4	8	10
Investment income									110	87	66
Total revenues									136	130	114
Benefits									77	131	617
Operating costs									6	12	16
Merger termination fee and related costs, net										0	0
Depreciation and amortization									0	0	1
Total operating expenses									83	143	634
Income from operations									53	(13)	(520)
Loss on sale of business									0		0
Interest expense									0	0	0
Other expense, net									0
Income (loss) before income taxes and equity in net earnings									53	(13)	(520)
Equity in net earnings of Kindred at Home									0	0	0
Segment earnings (losses)									53	(13)	(520)
Other Businesses | Individual Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									0	0	0
Other Businesses | Group Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									0	0	0
Other Businesses | Medicare stand-alone PDP
Segment Reporting Information [Line Items]
Premiums									0	0	0
Other Businesses | Total Medicare
Segment Reporting Information [Line Items]
Premiums									0	0	0
Other Businesses | Fully-insured
Segment Reporting Information [Line Items]
Premiums									0	0	0
Other Businesses | Specialty
Segment Reporting Information [Line Items]
Premiums									0	0	0
Other Businesses | Medicaid and other
Segment Reporting Information [Line Items]
Premiums									22	35	38
Other Businesses | Provider
Segment Reporting Information [Line Items]
Services									0	0	0
Other Businesses | ASO and other
Segment Reporting Information [Line Items]
Services									4	8	10
Other Businesses | Pharmacy
Segment Reporting Information [Line Items]
Services									0	0	0
Other Businesses | External Customers
Segment Reporting Information [Line Items]
Total revenues									26	43	48
Corporate/Eliminations
Segment Reporting Information [Line Items]
Services										0
Investment income									211	158	173
Total revenues									(22,977)	(23,447)	(24,821)
Benefits									(470)	(760)	(927)
Operating costs									(22,527)	(22,376)	(23,894)
Merger termination fee and related costs, net										(936)	104
Depreciation and amortization									(116)	(100)	(104)
Total operating expenses									(23,113)	(24,172)	(24,821)
Income from operations									136	725	0
Loss on sale of business									(786)		0
Interest expense									218	242	189
Other expense, net									(33)
Income (loss) before income taxes and equity in net earnings									(901)	483	(189)
Equity in net earnings of Kindred at Home									0	0	0
Segment earnings (losses)									(901)	483	(189)
Corporate/Eliminations | Provider
Segment Reporting Information [Line Items]
Services										0
Corporate/Eliminations | ASO and other
Segment Reporting Information [Line Items]
Services										0
Corporate/Eliminations | Pharmacy
Segment Reporting Information [Line Items]
Services										0
Corporate/Eliminations | External Customers
Segment Reporting Information [Line Items]
Total revenues										0
Intersegment revenues
Segment Reporting Information [Line Items]
Total revenues									(23,188)	(23,605)	(24,994)
Intersegment revenues | Retail
Segment Reporting Information [Line Items]
Total revenues									0	0	0
Intersegment revenues | Group and Specialty
Segment Reporting Information [Line Items]
Total revenues									18	20	22
Intersegment revenues | Healthcare Services
Segment Reporting Information [Line Items]
Total revenues									23,170	23,585	24,972
Intersegment revenues | Individual Commercial
Segment Reporting Information [Line Items]
Total revenues									0	0	0
Intersegment revenues | Services
Segment Reporting Information [Line Items]
Total revenues									(16,858)	(17,313)	(19,001)
Intersegment revenues | Services | Retail
Segment Reporting Information [Line Items]
Total revenues									0	0	0
Intersegment revenues | Services | Group and Specialty
Segment Reporting Information [Line Items]
Total revenues									18	20	22
Intersegment revenues | Services | Healthcare Services
Segment Reporting Information [Line Items]
Total revenues									16,840	17,293	18,979
Intersegment revenues | Services | Individual Commercial
Segment Reporting Information [Line Items]
Total revenues									0	0	0
Intersegment revenues | Products
Segment Reporting Information [Line Items]
Total revenues									(6,330)	(6,292)	(5,993)
Intersegment revenues | Products | Retail
Segment Reporting Information [Line Items]
Total revenues									0	0	0
Intersegment revenues | Products | Group and Specialty
Segment Reporting Information [Line Items]
Total revenues									0	0	0
Intersegment revenues | Products | Healthcare Services
Segment Reporting Information [Line Items]
Total revenues									6,330	6,292	5,993
Intersegment revenues | Products | Individual Commercial
Segment Reporting Information [Line Items]
Total revenues									$ 0	$ 0	$ 0