Changes in Carrying Amount of Goodwill by Reportable Segments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Goodwill [Line Items]
Beginning Balance	$ 2,740	$ 2,568
Acquisitions	894	169
Subsequent payments/adjustments	6	3
Ending Balance	3,640	2,740
Retail
Goodwill [Line Items]
Beginning Balance	754	593
Acquisitions	98	161
Subsequent payments/adjustments	(3)	0
Ending Balance	849	754
Employer Group
Goodwill [Line Items]
Beginning Balance	62	62
Acquisitions	0	0
Subsequent payments/adjustments	9	0
Ending Balance	71	62
Health And Well-Being Services
Goodwill [Line Items]
Beginning Balance	1,867	1,856
Acquisitions	753	8
Subsequent payments/adjustments	0	3
Ending Balance	2,620	1,867
Other Businesses
Goodwill [Line Items]
Beginning Balance	57	57
Acquisitions	43	0
Subsequent payments/adjustments	0	0
Ending Balance	$ 100	$ 57

Carrying amount as of the balance sheet date, which is the cumulative amount paid and (if applicable) the fair value of any noncontrolling interest in the acquiree, adjusted for any amortization recognized prior to the adoption of any changes in generally accepted accounting principles (as applicable) and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions.

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 45

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 34

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 43

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 45

-Subparagraph e

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 72

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

The aggregate amount of goodwill acquired in the period and allocated to the reportable segment. The value is stated at fair value based on the purchase price allocation.

+ References+ Details

- Definition

Change in the carrying value of goodwill. The change could be the result of new goodwill acquired, goodwill impairment, if any, goodwill written off related to the sale of a business or other adjustments to goodwill.

+ References+ Details