Segment Information by Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	$ 9,166	$ 8,849	$ 18,941	$ 17,616
Total services revenue	434	344	784	679
Total revenues-external customers	9,600	9,193	19,725	18,295
Total intersegment revenues	0	0	0	0
Investment income	99	91	193	180
Total revenues	9,699	9,284	19,918	18,475
Operating expenses, Benefits	7,652	7,269	16,002	14,614
Operating expenses, Operating costs	1,384	1,193	2,767	2,449
Operating expenses, Depreciation and amortization	73	68	143	134
Total operating expenses	9,109	8,530	18,912	17,197
Income (loss) from operations	590	754	1,006	1,278
Interest expense	26	28	52	55
Income (loss) before income taxes	564	726	954	1,223
Medicare Advantage
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	6,319	5,319	12,437	10,640
Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	747	680	1,475	1,315
Medicare
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	7,066	5,999	13,912	11,955
Fully-Insured
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	1,497	1,423	2,983	2,823
Specialty
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	304	263	602	519
Military Services
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	44	935	937	1,858
Medicaid And Other
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	255	229	507	461
Provider
Segment Reporting Information [Line Items]
Total services revenue	245	222	478	437
ASO And Other
Segment Reporting Information [Line Items]
Total services revenue	185	119	298	237
Pharmacy
Segment Reporting Information [Line Items]
Total services revenue	4	3	8	5
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	6,272	5,392	12,307	10,701
Total services revenue	5	4	11	7
Total revenues-external customers	6,277	5,396	12,318	10,708
Total intersegment revenues	1	0	1	0
Investment income	20	19	39	38
Total revenues	6,298	5,415	12,358	10,746
Operating expenses, Benefits	5,273	4,390	10,560	8,944
Operating expenses, Operating costs	625	490	1,253	1,023
Operating expenses, Depreciation and amortization	33	32	63	59
Total operating expenses	5,931	4,912	11,876	10,026
Income (loss) from operations	367	503	482	720
Interest expense	0	0	0	0
Income (loss) before income taxes	367	503	482	720
Retail | Medicare Advantage
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	5,308	4,555	10,401	9,080
Retail | Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	672	601	1,332	1,158
Retail | Medicare
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	5,980	5,156	11,733	10,238
Retail | Fully-Insured
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	250	206	494	407
Retail | Specialty
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	42	30	80	56
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	5	4	11	7
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	1	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	2,522	2,216	5,051	4,443
Total services revenue	89	87	178	180
Total revenues-external customers	2,611	2,303	5,229	4,623
Total intersegment revenues	4	3	8	6
Investment income	10	12	20	24
Total revenues	2,625	2,318	5,257	4,653
Operating expenses, Benefits	2,074	1,800	4,138	3,552
Operating expenses, Operating costs	417	387	844	811
Operating expenses, Depreciation and amortization	20	23	40	43
Total operating expenses	2,511	2,210	5,022	4,406
Income (loss) from operations	114	108	235	247
Interest expense	0	0	0	0
Income (loss) before income taxes	114	108	235	247
Employer Group | Medicare Advantage
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	1,011	764	2,036	1,560
Employer Group | Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	2	2	4	4
Employer Group | Medicare
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	1,013	766	2,040	1,564
Employer Group | Fully-Insured
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	1,247	1,217	2,489	2,416
Employer Group | Specialty
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	262	233	522	463
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	89	87	178	180
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	4	3	8	6
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	249	225	486	442
Total revenues-external customers	249	225	486	442
Total intersegment revenues	2,968	2,508	6,038	5,064
Investment income	0	0	0	0
Total revenues	3,217	2,733	6,524	5,506
Operating expenses, Benefits	0	0	0	0
Operating expenses, Operating costs	3,064	2,625	6,218	5,281
Operating expenses, Depreciation and amortization	22	20	43	40
Total operating expenses	3,086	2,645	6,261	5,321
Income (loss) from operations	131	88	263	185
Interest expense	0	0	0	0
Income (loss) before income taxes	131	88	263	185
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	245	222	478	437
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	4	3	8	5
Health And Well-Being Services | Services
Segment Reporting Information [Line Items]
Total intersegment revenues	2,377	2,074	4,863	4,195
Health And Well-Being Services | Products
Segment Reporting Information [Line Items]
Total intersegment revenues	591	434	1,175	869
Other Businesses
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	372	1,241	1,583	2,472
Total services revenue	91	28	109	50
Total revenues-external customers	463	1,269	1,692	2,522
Total intersegment revenues	0	0	0	0
Investment income	15	13	29	25
Total revenues	478	1,282	1,721	2,547
Operating expenses, Benefits	406	1,149	1,512	2,258
Operating expenses, Operating costs	123	111	239	230
Operating expenses, Depreciation and amortization	4	3	8	5
Total operating expenses	533	1,263	1,759	2,493
Income (loss) from operations	(55)	19	(38)	54
Interest expense	0	0	0	0
Income (loss) before income taxes	(55)	19	(38)	54
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	73	77	139	153
Other Businesses | Medicare
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	73	77	139	153
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	44	935	937	1,858
Other Businesses | Medicaid And Other
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	255	229	507	461
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	91	28	109	50
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	(2,973)	(2,511)	(6,047)	(5,070)
Investment income	54	47	105	93
Total revenues	(2,919)	(2,464)	(5,942)	(4,977)
Operating expenses, Benefits	(101)	(70)	(208)	(140)
Operating expenses, Operating costs	(2,845)	(2,420)	(5,787)	(4,896)
Operating expenses, Depreciation and amortization	(6)	(10)	(11)	(13)
Total operating expenses	(2,952)	(2,500)	(6,006)	(5,049)
Income (loss) from operations	33	36	64	72
Interest expense	26	28	52	55
Income (loss) before income taxes	7	8	12	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	(2,382)	(2,077)	(4,872)	(4,201)
Corporate Elimination | Products
Segment Reporting Information [Line Items]
Total intersegment revenues	$ (591)	$ (434)	$ (1,175)	$ (869)