Segment Information by Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	$ 9,701	$ 9,166	$ 19,569	$ 18,941
Total services revenue	528	434	1,053	784
Total revenues-external customers	10,229	9,600	20,622	19,725
Total intersegment revenues	0	0	0	0
Investment income	92	99	185	193
Total revenues	10,321	9,699	20,807	19,918
Operating expenses, Benefits	8,091	7,652	16,286	16,002
Operating expenses, Operating costs	1,461	1,384	2,907	2,767
Operating expenses, Depreciation and amortization	80	73	160	143
Total operating expenses	9,632	9,109	19,353	18,912
Income (loss) from operations	689	590	1,454	1,006
Interest expense	35	26	70	52
Income (loss) before income taxes	654	564	1,384	954
Medicare Advantage
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	6,732	6,319	13,658	12,437
Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	787	747	1,550	1,475
Medicare
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	7,519	7,066	15,208	13,912
Fully-Insured
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	1,558	1,497	3,105	2,983
Specialty
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	327	304	651	602
Military Services
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	5	44	16	937
Medicaid And Other
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	292	255	589	507
Provider
Segment Reporting Information [Line Items]
Total services revenue	317	245	627	478
Aso And Other
Segment Reporting Information [Line Items]
Total services revenue	198	185	404	298
Pharmacy
Segment Reporting Information [Line Items]
Total services revenue	13	4	22	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	6,766	6,390	13,670	12,537
Total services revenue	2	5	4	11
Total revenues-external customers	6,768	6,395	13,674	12,548
Total intersegment revenues	0	1	0	1
Investment income	18	20	36	39
Total revenues	6,786	6,416	13,710	12,588
Operating expenses, Benefits	5,696	5,378	11,625	10,755
Operating expenses, Operating costs	640	638	1,253	1,275
Operating expenses, Depreciation and amortization	32	33	64	63
Total operating expenses	6,368	6,049	12,942	12,093
Income (loss) from operations	418	367	768	495
Interest expense	0	0	0	0
Income (loss) before income taxes	418	367	768	495
Retail | Medicare Advantage
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	5,572	5,308	11,308	10,401
Retail | Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	785	745	1,546	1,471
Retail | Medicare
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	6,357	6,053	12,854	11,872
Retail | Fully-Insured
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	285	250	564	494
Retail | Specialty
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	52	42	101	80
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	72	45	151	91
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	2	5	4	11
Retail | Pharmacy
Segment Reporting Information [Line Items]
Total services revenue	0	0	0	0
Retail | Services
Segment Reporting Information [Line Items]
Total intersegment revenues	0	1	0	1
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	2,710	2,522	5,445	5,051
Total services revenue	86	91	174	182
Total revenues-external customers	2,796	2,613	5,619	5,233
Total intersegment revenues	12	7	23	17
Investment income	10	10	21	20
Total revenues	2,818	2,630	5,663	5,270
Operating expenses, Benefits	2,235	2,063	4,412	4,116
Operating expenses, Operating costs	429	428	869	864
Operating expenses, Depreciation and amortization	27	22	50	44
Total operating expenses	2,691	2,513	5,331	5,024
Income (loss) from operations	127	117	332	246
Interest expense	0	0	0	0
Income (loss) before income taxes	127	117	332	246
Employer Group | Medicare Advantage
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	1,160	1,011	2,350	2,036
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	1,162	1,013	2,354	2,040
Employer Group | Fully-Insured
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	1,273	1,247	2,541	2,489
Employer Group | Specialty
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	275	262	550	522
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	4	2	8	4
Employer Group | Aso And Other
Segment Reporting Information [Line Items]
Total services revenue	82	89	166	178
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	12	7	23	17
Employer Group | Products
Segment Reporting Information [Line Items]
Total intersegment revenues	0	0	0	0
Healthcare Services
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Total services revenue	326	247	641	482
Total revenues-external customers	326	247	641	482
Total intersegment revenues	3,538	2,950	6,941	5,999
Investment income	0	0	0	0
Total revenues	3,864	3,197	7,582	6,481
Operating expenses, Benefits	0	0	0	0
Operating expenses, Operating costs	3,697	3,049	7,254	6,189
Operating expenses, Depreciation and amortization	36	20	72	39
Total operating expenses	3,733	3,069	7,326	6,228
Income (loss) from operations	131	128	256	253
Interest expense	0	0	0	0
Income (loss) before income taxes	131	128	256	253
Healthcare Services | Medicare Advantage
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Healthcare Services | Medicare Stand Alone Prescription Drug Plan
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Healthcare Services | Medicare
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Healthcare Services | Fully-Insured
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Healthcare Services | Specialty
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Healthcare Services | Military Services
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Healthcare Services | Medicaid And Other
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
Healthcare Services | Provider
Segment Reporting Information [Line Items]
Total services revenue	313	243	619	474
Healthcare Services | Aso And Other
Segment Reporting Information [Line Items]
Total services revenue	0	0	0	0
Healthcare Services | Pharmacy
Segment Reporting Information [Line Items]
Total services revenue	13	4	22	8
Healthcare Services | Services
Segment Reporting Information [Line Items]
Total intersegment revenues	2,858	2,359	5,607	4,824
Healthcare Services | Products
Segment Reporting Information [Line Items]
Total intersegment revenues	680	591	1,334	1,175
Other Businesses
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	225	254	454	1,353
Total services revenue	114	91	234	109
Total revenues-external customers	339	345	688	1,462
Total intersegment revenues	0	0	0	0
Investment income	15	15	30	29
Total revenues	354	360	718	1,491
Operating expenses, Benefits	251	301	438	1,317
Operating expenses, Operating costs	129	111	244	217
Operating expenses, Depreciation and amortization	4	4	8	8
Total operating expenses	384	416	690	1,542
Income (loss) from operations	(30)	(56)	28	(51)
Interest expense	0	0	0	0
Income (loss) before income taxes	(30)	(56)	28	(51)
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	0	0	0	0
Other Businesses | Medicare
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	0	0	0	0
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	5	44	16	937
Other Businesses | Medicaid And Other
Segment Reporting Information [Line Items]
Revenues-external customers, Premiums	220	210	438	416
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	114	91	234	109
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	(3,550)	(2,958)	(6,964)	(6,017)
Investment income	49	54	98	105
Total revenues	(3,501)	(2,904)	(6,866)	(5,912)
Operating expenses, Benefits	(91)	(90)	(189)	(186)
Operating expenses, Operating costs	(3,434)	(2,842)	(6,713)	(5,778)
Operating expenses, Depreciation and amortization	(19)	(6)	(34)	(11)
Total operating expenses	(3,544)	(2,938)	(6,936)	(5,975)
Income (loss) from operations	43	34	70	63
Interest expense	35	26	70	52
Income (loss) before income taxes	8	8	0	11
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	(2,870)	(2,367)	(5,630)	(4,842)
Corporate Elimination | Products
Segment Reporting Information [Line Items]
Total intersegment revenues	$ (680)	$ (591)	$ (1,334)	$ (1,175)