Acquisitions - identified definite and indefinite-lived intangible assets (Details) - Alliance Boots $ in Millions	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Amount	$ 2,545
Amount	$ 9,146
Customer relationships
Business Acquisition [Line Items]
Weighted-average useful life	12 years
Amount	$ 1,311
Loyalty card holders
Business Acquisition [Line Items]
Weighted-average useful life	20 years
Amount	$ 742
Trade names and trademarks
Business Acquisition [Line Items]
Weighted-average useful life	9 years
Amount	$ 399
Favorable lease interests
Business Acquisition [Line Items]
Weighted-average useful life	7 years
Amount	$ 93
Trade names and trademarks
Business Acquisition [Line Items]
Amount	6,657
Pharmacy licenses
Business Acquisition [Line Items]
Amount	$ 2,489

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275

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