Segment Information by Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	$ 9,088	$ 8,852	$ 28,029	$ 26,468
Total services revenue	467	356	1,251	1,035
Total revenues-external customers	9,555	9,208	29,280	27,503
Total intersegment revenues	0	0	0	0
Investment income	96	93	289	273
Total revenues	9,651	9,301	29,569	27,776
Operating expenses, Benefits	7,467	7,147	23,469	21,761
Operating expenses, Operating costs	1,408	1,361	4,175	3,810
Operating expenses, depreciation and amortization	75	67	218	201
Total operating expenses	8,950	8,575	27,862	25,772
Income (loss) from operations	701	726	1,707	2,004
Interest expense	26	27	78	82
Income (loss) before income taxes	675	699	1,629	1,922
Medicare Advantage
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	6,226	5,369	18,663	16,009
Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	701	624	2,176	1,939
Medicare
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	6,927	5,993	20,839	17,948
Fully-Insured
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	1,511	1,406	4,494	4,229
Specialty
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	316	268	918	787
Military Services
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	69	944	1,006	2,802
Medicaid And Other
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	265	241	772	702
Provider
Segment Reporting Information [Line Items]
Total services revenue	271	233	749	670
Aso And Other
Segment Reporting Information [Line Items]
Total services revenue	193	120	491	357
Pharmacy
Segment Reporting Information [Line Items]
Total services revenue	3	3	11	8
Services
Segment Reporting Information [Line Items]
Total intersegment revenues	0	0	0	0
Products
Segment Reporting Information [Line Items]
Total intersegment revenues	0	0	0	0
Retail
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	6,138	5,399	18,445	16,100
Total services revenue	6	5	17	12
Total revenues-external customers	6,144	5,404	18,462	16,112
Total intersegment revenues	1	0	2	0
Investment income	19	19	58	57
Total revenues	6,164	5,423	18,522	16,169
Operating expenses, Benefits	5,049	4,249	15,609	13,193
Operating expenses, Operating costs	658	603	1,911	1,626
Operating expenses, depreciation and amortization	33	30	96	89
Total operating expenses	5,740	4,882	17,616	14,908
Income (loss) from operations	424	541	906	1,261
Interest expense	0	0	0	0
Income (loss) before income taxes	424	541	906	1,261
Retail | Medicare Advantage
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	5,203	4,566	15,604	13,646
Retail | Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	635	579	1,967	1,737
Retail | Medicare
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	5,838	5,145	17,571	15,383
Retail | Fully-Insured
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	255	221	749	628
Retail | Specialty
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	45	33	125	89
Retail | Military Services
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Retail | Medicaid And Other
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Retail | Provider
Segment Reporting Information [Line Items]
Total services revenue	0	0	0	0
Retail | Aso And Other
Segment Reporting Information [Line Items]
Total services revenue	6	5	17	12
Retail | Pharmacy
Segment Reporting Information [Line Items]
Total services revenue	0	0	0	0
Retail | Services
Segment Reporting Information [Line Items]
Total intersegment revenues	1	0	2	0
Retail | Products
Segment Reporting Information [Line Items]
Total intersegment revenues	0	0	0	0
Employer Group
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	2,552	2,225	7,603	6,668
Total services revenue	88	89	266	269
Total revenues-external customers	2,640	2,314	7,869	6,937
Total intersegment revenues	3	4	11	10
Investment income	11	12	31	36
Total revenues	2,654	2,330	7,911	6,983
Operating expenses, Benefits	2,178	1,857	6,316	5,409
Operating expenses, Operating costs	413	406	1,257	1,217
Operating expenses, depreciation and amortization	20	21	60	64
Total operating expenses	2,611	2,284	7,633	6,690
Income (loss) from operations	43	46	278	293
Interest expense	0	0	0	0
Income (loss) before income taxes	43	46	278	293
Employer Group | Medicare Advantage
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	1,023	803	3,059	2,363
Employer Group | Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	2	2	6	6
Employer Group | Medicare
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	1,025	805	3,065	2,369
Employer Group | Fully-Insured
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	1,256	1,185	3,745	3,601
Employer Group | Specialty
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	271	235	793	698
Employer Group | Military Services
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Employer Group | Medicaid And Other
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Employer Group | Provider
Segment Reporting Information [Line Items]
Total services revenue	0	0	0	0
Employer Group | Aso And Other
Segment Reporting Information [Line Items]
Total services revenue	88	89	266	269
Employer Group | Pharmacy
Segment Reporting Information [Line Items]
Total services revenue	0	0	0	0
Employer Group | Services
Segment Reporting Information [Line Items]
Total intersegment revenues	3	4	11	10
Employer Group | Products
Segment Reporting Information [Line Items]
Total intersegment revenues	0	0	0	0
Health And Well-Being Services
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Total services revenue	274	236	760	678
Total revenues-external customers	274	236	760	678
Total intersegment revenues	2,926	2,591	8,964	7,655
Investment income	0	0	0	0
Total revenues	3,200	2,827	9,724	8,333
Operating expenses, Benefits	0	0	0	0
Operating expenses, Operating costs	3,028	2,723	9,246	8,004
Operating expenses, depreciation and amortization	24	21	67	61
Total operating expenses	3,052	2,744	9,313	8,065
Income (loss) from operations	148	83	411	268
Interest expense	0	0	0	0
Income (loss) before income taxes	148	83	411	268
Health And Well-Being Services | Medicare Advantage
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Health And Well-Being Services | Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Health And Well-Being Services | Medicare
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Health And Well-Being Services | Fully-Insured
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Health And Well-Being Services | Specialty
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Health And Well-Being Services | Military Services
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Health And Well-Being Services | Medicaid And Other
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Health And Well-Being Services | Provider
Segment Reporting Information [Line Items]
Total services revenue	271	233	749	670
Health And Well-Being Services | Aso And Other
Segment Reporting Information [Line Items]
Total services revenue	0	0	0	0
Health And Well-Being Services | Pharmacy
Segment Reporting Information [Line Items]
Total services revenue	3	3	11	8
Health And Well-Being Services | Services
Segment Reporting Information [Line Items]
Total intersegment revenues	2,324	2,130	7,187	6,325
Health And Well-Being Services | Products
Segment Reporting Information [Line Items]
Total intersegment revenues	602	461	1,777	1,330
Other Businesses
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	398	1,228	1,981	3,700
Total services revenue	99	26	208	76
Total revenues-external customers	497	1,254	2,189	3,776
Total intersegment revenues	0	0	0	0
Investment income	14	15	43	40
Total revenues	511	1,269	2,232	3,816
Operating expenses, Benefits	332	1,117	1,844	3,375
Operating expenses, Operating costs	125	121	364	351
Operating expenses, depreciation and amortization	4	2	12	7
Total operating expenses	461	1,240	2,220	3,733
Income (loss) from operations	50	29	12	83
Interest expense	0	0	0	0
Income (loss) before income taxes	50	29	12	83
Other Businesses | Medicare Advantage
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Other Businesses | Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	64	43	203	196
Other Businesses | Medicare
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	64	43	203	196
Other Businesses | Fully-Insured
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Other Businesses | Specialty
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Other Businesses | Military Services
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	69	944	1,006	2,802
Other Businesses | Medicaid And Other
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	265	241	772	702
Other Businesses | Provider
Segment Reporting Information [Line Items]
Total services revenue	0	0	0	0
Other Businesses | Aso And Other
Segment Reporting Information [Line Items]
Total services revenue	99	26	208	76
Other Businesses | Pharmacy
Segment Reporting Information [Line Items]
Total services revenue	0	0	0	0
Other Businesses | Services
Segment Reporting Information [Line Items]
Total intersegment revenues	0	0	0	0
Other Businesses | Products
Segment Reporting Information [Line Items]
Total intersegment revenues	0	0	0	0
Corporate Elimination
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Total services revenue	0	0	0	0
Total revenues-external customers	0	0	0	0
Total intersegment revenues	(2,930)	(2,595)	(8,977)	(7,665)
Investment income	52	47	157	140
Total revenues	(2,878)	(2,548)	(8,820)	(7,525)
Operating expenses, Benefits	(92)	(76)	(300)	(216)
Operating expenses, Operating costs	(2,816)	(2,492)	(8,603)	(7,388)
Operating expenses, depreciation and amortization	(6)	(7)	(17)	(20)
Total operating expenses	(2,914)	(2,575)	(8,920)	(7,624)
Income (loss) from operations	36	27	100	99
Interest expense	26	27	78	82
Income (loss) before income taxes	10	0	22	17
Corporate Elimination | Medicare Advantage
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Corporate Elimination | Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Corporate Elimination | Medicare
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Corporate Elimination | Fully-Insured
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Corporate Elimination | Specialty
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Corporate Elimination | Military Services
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Corporate Elimination | Medicaid And Other
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Corporate Elimination | Provider
Segment Reporting Information [Line Items]
Total services revenue	0	0	0	0
Corporate Elimination | Aso And Other
Segment Reporting Information [Line Items]
Total services revenue	0	0	0	0
Corporate Elimination | Pharmacy
Segment Reporting Information [Line Items]
Total services revenue	0	0	0	0
Corporate Elimination | Services
Segment Reporting Information [Line Items]
Total intersegment revenues	(2,328)	(2,134)	(7,200)	(6,335)
Corporate Elimination | Products
Segment Reporting Information [Line Items]
Total intersegment revenues	$ (602)	$ (461)	$ (1,777)	$ (1,330)