Capital transactions (Details 2) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	4 Months Ended	5 Months Ended	6 Months Ended	7 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	May 16, 2012	Jun. 01, 2012	Jun. 30, 2011	Aug. 12, 2011	Sep. 30, 2012	Sep. 30, 2011
Share Repurchase Program
Dividends per common share (in dollars per share)	$ 0	$ 0					$ 0.18	$ 0.165
Cash dividend payment			$ 201	$ 3	$ 192	$ 2	$ 204	$ 194

The cash outflow from the distribution of an entity's earnings in the form of dividends to common shareholders.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3291-108585

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 18

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 20

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

Name:	us-gaap_PaymentsOfDividendsCommonStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration