Segment Information by Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Premiums									$ 45,959	$ 38,829	$ 37,009
Services									2,164	2,109	1,726
Total revenues-external customers									48,123	40,938	38,735
Total revenues	12,328	12,238	12,222	11,712	10,187	10,319	10,321	10,486	48,500	41,313	39,126
Investment income									377	375	391
Benefits									38,166	32,564	30,985
Operating costs									7,639	6,355	5,830
Depreciation and amortization									333	333	295
Total operating expenses									46,138	39,252	37,110
Income from operations									2,362	2,061	2,016
Interest expense									192	140	105
Income before income taxes	287	551	646	686	(49)	586	654	730	2,170	1,921	1,911
Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									31,431	27,191	24,852
Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Premiums									3,404	3,033	2,861
Medicare
Segment Reporting Information [Line Items]
Premiums									34,835	30,224	27,713
Fully-Insured
Segment Reporting Information [Line Items]
Premiums									8,604	6,277	6,000
Specialty
Segment Reporting Information [Line Items]
Premiums									1,354	1,305	1,241
Military Services
Segment Reporting Information [Line Items]
Premiums									19	25	1,017
Medicaid And Other
Segment Reporting Information [Line Items]
Premiums									1,147	998	1,038
Provider
Segment Reporting Information [Line Items]
Services									1,206	1,242	1,020
Aso And Other
Segment Reporting Information [Line Items]
Services									859	808	690
Pharmacy
Segment Reporting Information [Line Items]
Services									99	59	16
Intersegment revenues
Segment Reporting Information [Line Items]
Total revenues									(18,811)	(14,662)	(12,055)
Intersegment revenues | Retail
Segment Reporting Information [Line Items]
Total revenues									0	0	2
Intersegment revenues | Employer Group
Segment Reporting Information [Line Items]
Total revenues									78	51	31
Intersegment revenues | Healthcare Services
Segment Reporting Information [Line Items]
Total revenues									18,733	14,611	12,022
Intersegment revenues | Other Businesses
Segment Reporting Information [Line Items]
Total revenues									0	0	0
Intersegment revenues | Services
Segment Reporting Information [Line Items]
Total revenues									(15,062)	(11,859)	(9,713)
Intersegment revenues | Services | Retail
Segment Reporting Information [Line Items]
Total revenues									0	0	2
Intersegment revenues | Services | Employer Group
Segment Reporting Information [Line Items]
Total revenues									78	51	31
Intersegment revenues | Services | Healthcare Services
Segment Reporting Information [Line Items]
Total revenues									14,984	11,808	9,680
Intersegment revenues | Services | Other Businesses
Segment Reporting Information [Line Items]
Total revenues									0	0	0
Intersegment revenues | Products
Segment Reporting Information [Line Items]
Total revenues									(3,749)	(2,803)	(2,342)
Intersegment revenues | Products | Retail
Segment Reporting Information [Line Items]
Total revenues									0	0	0
Intersegment revenues | Products | Employer Group
Segment Reporting Information [Line Items]
Total revenues									0	0	0
Intersegment revenues | Products | Healthcare Services
Segment Reporting Information [Line Items]
Total revenues									3,749	2,803	2,342
Intersegment revenues | Products | Other Businesses
Segment Reporting Information [Line Items]
Total revenues									0	0	0
Operating Segments | Retail
Segment Reporting Information [Line Items]
Premiums									33,954	27,204	25,001
Services									39	16	24
Total revenues-external customers									33,993	27,220	25,025
Total revenues									34,069	27,294	25,106
Investment income									76	74	79
Benefits									28,608	22,914	21,048
Operating costs									4,209	2,963	2,767
Depreciation and amortization									154	134	130
Total operating expenses									32,971	26,011	23,945
Income from operations									1,098	1,283	1,161
Interest expense									0	0	0
Income before income taxes									1,098	1,283	1,161
Operating Segments | Employer Group
Segment Reporting Information [Line Items]
Premiums									11,935	10,930	10,138
Services									362	359	371
Total revenues-external customers									12,297	11,289	10,509
Total revenues									12,419	11,382	10,582
Investment income									44	42	42
Benefits									10,019	9,124	8,471
Operating costs									1,987	1,806	1,710
Depreciation and amortization									99	102	89
Total operating expenses									12,105	11,032	10,270
Income from operations									314	350	312
Interest expense									0	0	0
Income before income taxes									314	350	312
Operating Segments | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Services									1,282	1,280	1,023
Total revenues-external customers									1,282	1,280	1,023
Total revenues									20,015	15,891	13,045
Investment income									0	0	0
Benefits									0	0	0
Operating costs									19,121	15,223	12,530
Depreciation and amortization									155	147	87
Total operating expenses									19,276	15,370	12,617
Income from operations									739	521	428
Interest expense									0	0	0
Income before income taxes									739	521	428
Operating Segments | Other Businesses
Segment Reporting Information [Line Items]
Premiums									70	695	1,870
Services									481	454	308
Total revenues-external customers									551	1,149	2,178
Total revenues									611	1,208	2,236
Investment income									60	59	58
Benefits									113	935	1,802
Operating costs									405	446	436
Depreciation and amortization									15	20	16
Total operating expenses									533	1,401	2,254
Income from operations									78	(193)	(18)
Interest expense									0	0	0
Income before income taxes									78	(193)	(18)
Operating Segments | Medicare Advantage | Retail
Segment Reporting Information [Line Items]
Premiums									25,941	22,481	20,788
Operating Segments | Medicare Advantage | Employer Group
Segment Reporting Information [Line Items]
Premiums									5,490	4,710	4,064
Operating Segments | Medicare Advantage | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Medicare Advantage | Other Businesses
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Medicare Stand Alone Prescription Drug Plan | Retail
Segment Reporting Information [Line Items]
Premiums									3,396	3,025	2,853
Operating Segments | Medicare Stand Alone Prescription Drug Plan | Employer Group
Segment Reporting Information [Line Items]
Premiums									8	8	8
Operating Segments | Medicare Stand Alone Prescription Drug Plan | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Medicare Stand Alone Prescription Drug Plan | Other Businesses
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Medicare | Retail
Segment Reporting Information [Line Items]
Premiums									29,337	25,506	23,641
Operating Segments | Medicare | Employer Group
Segment Reporting Information [Line Items]
Premiums									5,498	4,718	4,072
Operating Segments | Medicare | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Medicare | Other Businesses
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Fully-Insured | Retail
Segment Reporting Information [Line Items]
Premiums									3,265	1,160	1,004
Operating Segments | Fully-Insured | Employer Group
Segment Reporting Information [Line Items]
Premiums									5,339	5,117	4,996
Operating Segments | Fully-Insured | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Fully-Insured | Other Businesses
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Specialty | Retail
Segment Reporting Information [Line Items]
Premiums									256	210	171
Operating Segments | Specialty | Employer Group
Segment Reporting Information [Line Items]
Premiums									1,098	1,095	1,070
Operating Segments | Specialty | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Specialty | Other Businesses
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Military Services | Retail
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Military Services | Employer Group
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Military Services | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Military Services | Other Businesses
Segment Reporting Information [Line Items]
Premiums									19	25	1,017
Operating Segments | Medicaid And Other | Retail
Segment Reporting Information [Line Items]
Premiums									1,096	328	185
Operating Segments | Medicaid And Other | Employer Group
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Medicaid And Other | Healthcare Services
Segment Reporting Information [Line Items]
Premiums									0	0	0
Operating Segments | Medicaid And Other | Other Businesses
Segment Reporting Information [Line Items]
Premiums									51	670	853
Operating Segments | Provider | Retail
Segment Reporting Information [Line Items]
Services									0	0	0
Operating Segments | Provider | Employer Group
Segment Reporting Information [Line Items]
Services									23	21	13
Operating Segments | Provider | Healthcare Services
Segment Reporting Information [Line Items]
Services									1,183	1,221	1,007
Operating Segments | Provider | Other Businesses
Segment Reporting Information [Line Items]
Services									0	0	0
Operating Segments | Aso And Other | Retail
Segment Reporting Information [Line Items]
Services									39	16	24
Operating Segments | Aso And Other | Employer Group
Segment Reporting Information [Line Items]
Services									339	338	358
Operating Segments | Aso And Other | Healthcare Services
Segment Reporting Information [Line Items]
Services									0	0	0
Operating Segments | Aso And Other | Other Businesses
Segment Reporting Information [Line Items]
Services									481	454	308
Operating Segments | Pharmacy | Retail
Segment Reporting Information [Line Items]
Services									0	0	0
Operating Segments | Pharmacy | Employer Group
Segment Reporting Information [Line Items]
Services									0	0	0
Operating Segments | Pharmacy | Healthcare Services
Segment Reporting Information [Line Items]
Services									99	59	16
Operating Segments | Pharmacy | Other Businesses
Segment Reporting Information [Line Items]
Services									0	0	0
Eliminations/Corporate
Segment Reporting Information [Line Items]
Premiums									0	0	0
Services									0	0	0
Total revenues-external customers									0	0	0
Total revenues									(18,614)	(14,462)	(11,843)
Investment income									197	200	212
Benefits									(574)	(409)	(336)
Operating costs									(18,083)	(14,083)	(11,613)
Depreciation and amortization									(90)	(70)	(27)
Total operating expenses									(18,747)	(14,562)	(11,976)
Income from operations									133	100	133
Interest expense									192	140	105
Income before income taxes									(59)	(40)	28
Eliminations/Corporate | Medicare Advantage
Segment Reporting Information [Line Items]
Premiums									0	0	0
Eliminations/Corporate | Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Premiums									0	0	0
Eliminations/Corporate | 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 | Military Services
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									0	0	0
Eliminations/Corporate | Aso And Other
Segment Reporting Information [Line Items]
Services									0	0	0
Eliminations/Corporate | Pharmacy
Segment Reporting Information [Line Items]
Services									$ 0	$ 0	$ 0