Segment Information by Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]
Premiums	$ 9,698	$ 9,088	$ 29,267	$ 28,029
Services	528	467	1,581	1,251
Total revenues-external customers	10,226	9,555	30,848	29,280
Investment income	93	96	278	289
Total revenues	10,319	9,651	31,126	29,569
Benefits	8,075	7,467	24,361	23,469
Operating costs	1,540	1,408	4,447	4,175
Depreciation and amortization	83	75	243	218
Total operating expenses	9,698	8,950	29,051	27,862
Income from operations	621	701	2,075	1,707
Interest expense	35	26	105	78
Income before income taxes	586	675	1,970	1,629
Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	6,745	6,226	20,403	18,663
Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Premiums	742	701	2,292	2,176
Medicare
Segment Reporting Information [Line Items]
Premiums	7,487	6,927	22,695	20,839
Fully-Insured
Segment Reporting Information [Line Items]
Premiums	1,570	1,511	4,675	4,494
Specialty
Segment Reporting Information [Line Items]
Premiums	327	316	978	918
Military Services
Segment Reporting Information [Line Items]
Premiums	6	69	22	1,006
Medicaid And Other
Segment Reporting Information [Line Items]
Premiums	308	265	897	772
Provider
Segment Reporting Information [Line Items]
Services	316	271	943	749
Aso And Other
Segment Reporting Information [Line Items]
Services	195	193	599	491
Pharmacy
Segment Reporting Information [Line Items]
Services	17	3	39	11
Intersegment revenues
Segment Reporting Information [Line Items]
Total revenues	(3,679)	(2,914)	(10,643)	(8,931)
Intersegment revenues | Retail
Segment Reporting Information [Line Items]
Total revenues	0	1	0	2
Intersegment revenues | Employer Group
Segment Reporting Information [Line Items]
Total revenues	14	5	37	22
Intersegment revenues | Healthcare Services
Segment Reporting Information [Line Items]
Total revenues	3,665	2,908	10,606	8,907
Intersegment revenues | Other Businesses
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Intersegment revenues | Services
Segment Reporting Information [Line Items]
Total revenues	(2,963)	(2,312)	(8,593)	(7,154)
Intersegment revenues | Services | Retail
Segment Reporting Information [Line Items]
Total revenues	0	1	0	2
Intersegment revenues | Services | Employer Group
Segment Reporting Information [Line Items]
Total revenues	14	5	37	22
Intersegment revenues | Services | Healthcare Services
Segment Reporting Information [Line Items]
Total revenues	2,949	2,306	8,556	7,130
Intersegment revenues | Services | Other Businesses
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Intersegment revenues | Products
Segment Reporting Information [Line Items]
Total revenues	(716)	(602)	(2,050)	(1,777)
Intersegment revenues | Products | Retail
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Intersegment revenues | Products | Employer Group
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Intersegment revenues | Products | Healthcare Services
Segment Reporting Information [Line Items]
Total revenues	716	602	2,050	1,777
Intersegment revenues | Products | Other Businesses
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Operating Segments | Retail
Segment Reporting Information [Line Items]
Premiums	6,714	6,249	20,384	18,786
Services	3	6	7	17
Total revenues-external customers	6,717	6,255	20,391	18,803
Investment income	19	19	55	58
Total revenues	6,736	6,275	20,446	18,863
Benefits	5,647	5,150	17,272	15,905
Operating costs	718	675	1,971	1,950
Depreciation and amortization	33	32	97	95
Total operating expenses	6,398	5,857	19,340	17,950
Income from operations	338	418	1,106	913
Interest expense	0	0	0	0
Income before income taxes	338	418	1,106	913
Operating Segments | Employer Group
Segment Reporting Information [Line Items]
Premiums	2,746	2,552	8,191	7,603
Services	89	91	263	273
Total revenues-external customers	2,835	2,643	8,454	7,876
Investment income	10	11	31	31
Total revenues	2,859	2,659	8,522	7,929
Benefits	2,316	2,168	6,728	6,284
Operating costs	449	421	1,318	1,285
Depreciation and amortization	25	23	75	67
Total operating expenses	2,790	2,612	8,121	7,636
Income from operations	69	47	401	293
Interest expense	0	0	0	0
Income before income taxes	69	47	401	293
Operating Segments | Healthcare Services
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Services	328	271	969	753
Total revenues-external customers	328	271	969	753
Investment income	0	0	0	0
Total revenues	3,993	3,179	11,575	9,660
Benefits	0	0	0	0
Operating costs	3,800	3,013	11,054	9,202
Depreciation and amortization	37	22	109	61
Total operating expenses	3,837	3,035	11,163	9,263
Income from operations	156	144	412	397
Interest expense	0	0	0	0
Income before income taxes	156	144	412	397
Operating Segments | Other Businesses
Segment Reporting Information [Line Items]
Premiums	238	287	692	1,640
Services	108	99	342	208
Total revenues-external customers	346	386	1,034	1,848
Investment income	15	14	45	43
Total revenues	361	400	1,079	1,891
Benefits	230	232	668	1,549
Operating costs	103	108	347	325
Depreciation and amortization	5	4	13	12
Total operating expenses	338	344	1,028	1,886
Income from operations	23	56	51	5
Interest expense	0	0	0	0
Income before income taxes	23	56	51	5
Operating Segments | Medicare Advantage | Retail
Segment Reporting Information [Line Items]
Premiums	5,552	5,203	16,860	15,604
Operating Segments | Medicare Advantage | Employer Group
Segment Reporting Information [Line Items]
Premiums	1,193	1,023	3,543	3,059
Operating Segments | Medicare Advantage | Healthcare Services
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Medicare Advantage | Other Businesses
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Medicare Stand Alone Prescription Drug Plan | Retail
Segment Reporting Information [Line Items]
Premiums	740	699	2,286	2,170
Operating Segments | Medicare Stand Alone Prescription Drug Plan | Employer Group
Segment Reporting Information [Line Items]
Premiums	2	2	6	6
Operating Segments | Medicare Stand Alone Prescription Drug Plan | Healthcare Services
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Medicare Stand Alone Prescription Drug Plan | Other Businesses
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Medicare | Retail
Segment Reporting Information [Line Items]
Premiums	6,292	5,902	19,146	17,774
Operating Segments | Medicare | Employer Group
Segment Reporting Information [Line Items]
Premiums	1,195	1,025	3,549	3,065
Operating Segments | Medicare | Healthcare Services
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Medicare | Other Businesses
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Fully-Insured | Retail
Segment Reporting Information [Line Items]
Premiums	292	255	856	749
Operating Segments | Fully-Insured | Employer Group
Segment Reporting Information [Line Items]
Premiums	1,278	1,256	3,819	3,745
Operating Segments | Fully-Insured | Healthcare Services
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Fully-Insured | Other Businesses
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Specialty | Retail
Segment Reporting Information [Line Items]
Premiums	54	45	155	125
Operating Segments | Specialty | Employer Group
Segment Reporting Information [Line Items]
Premiums	273	271	823	793
Operating Segments | Specialty | Healthcare Services
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Specialty | Other Businesses
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Military Services | Retail
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Military Services | Employer Group
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Military Services | Healthcare Services
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Military Services | Other Businesses
Segment Reporting Information [Line Items]
Premiums	6	69	22	1,006
Operating Segments | Medicaid And Other | Retail
Segment Reporting Information [Line Items]
Premiums	76	47	227	138
Operating Segments | Medicaid And Other | Employer Group
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Medicaid And Other | Healthcare Services
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Operating Segments | Medicaid And Other | Other Businesses
Segment Reporting Information [Line Items]
Premiums	232	218	670	634
Operating Segments | Provider | Retail
Segment Reporting Information [Line Items]
Services	0	0	0	0
Operating Segments | Provider | Employer Group
Segment Reporting Information [Line Items]
Services	5	3	13	7
Operating Segments | Provider | Healthcare Services
Segment Reporting Information [Line Items]
Services	311	268	930	742
Operating Segments | Provider | Other Businesses
Segment Reporting Information [Line Items]
Services	0	0	0	0
Operating Segments | Aso And Other | Retail
Segment Reporting Information [Line Items]
Services	3	6	7	17
Operating Segments | Aso And Other | Employer Group
Segment Reporting Information [Line Items]
Services	84	88	250	266
Operating Segments | Aso And Other | Healthcare Services
Segment Reporting Information [Line Items]
Services	0	0	0	0
Operating Segments | Aso And Other | Other Businesses
Segment Reporting Information [Line Items]
Services	108	99	342	208
Operating Segments | Pharmacy | Retail
Segment Reporting Information [Line Items]
Services	0	0	0	0
Operating Segments | Pharmacy | Employer Group
Segment Reporting Information [Line Items]
Services	0	0	0	0
Operating Segments | Pharmacy | Healthcare Services
Segment Reporting Information [Line Items]
Services	17	3	39	11
Operating Segments | Pharmacy | Other Businesses
Segment Reporting Information [Line Items]
Services	0	0	0	0
Eliminations/Corporate
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Services	0	0	0	0
Total revenues-external customers	0	0	0	0
Investment income	49	52	147	157
Total revenues	(3,630)	(2,862)	(10,496)	(8,774)
Benefits	(118)	(83)	(307)	(269)
Operating costs	(3,530)	(2,809)	(10,243)	(8,587)
Depreciation and amortization	(17)	(6)	(51)	(17)
Total operating expenses	(3,665)	(2,898)	(10,601)	(8,873)
Income from operations	35	36	105	99
Interest expense	35	26	105	78
Income before income taxes	0	10	0	21
Eliminations/Corporate | Medicare Advantage
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Eliminations/Corporate | Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Premiums	0	0	0	0
Eliminations/Corporate | 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 | Military Services
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	0	0	0	0
Eliminations/Corporate | Aso And Other
Segment Reporting Information [Line Items]
Services	0	0	0	0
Eliminations/Corporate | Pharmacy
Segment Reporting Information [Line Items]
Services	$ 0	$ 0	$ 0	$ 0