The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 1A

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number APB14-1

-Paragraph 31

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

Name:	us-gaap_DebtInstrumentUnamortizedDiscount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Financing arrangements Financing arrangements (Details 1) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of 2013 convertible notes [Abstract]
Principal balance	$ 5,000	$ 10,500	$ 2,500
0.375% convertible notes due 2013 (0.375% 2013 Convertible Notes) [Member]
Schedule of 2013 convertible notes [Abstract]
Principal balance	2,500
Net carrying amount	2,488
Net carrying amount		2,346
0.375% convertible notes due 2013 (0.375% 2013 Convertible Notes) [Member] \| Liability Component [Member]
Schedule of 2013 convertible notes [Abstract]
Principal balance	2,500	2,500
Unamortized discount	12	154
Net carrying amount	2,488
Net carrying amount		2,346
0.375% convertible notes due 2013 (0.375% 2013 Convertible Notes) [Member] \| Equity Component [Member]
Schedule of 2013 convertible notes [Abstract]
Net carrying amount	$ 829	$ 829