Capital transactions (Details 2) (USD $) In Millions, except Per Share data	3 Months Ended	6 Months Ended
Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Share Repurchase Program [Abstract]
Dividends per common share (in dollars per share)	$ 0		$ 0	$ 0.165	$ 0.15
Cash dividend payment	$ 192	$ 2	$ 187	$ 192	$ 187

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 Statement of Financial Accounting Standard (FAS)
-Number 95
-Paragraph 18

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 95
-Paragraph 20
-Subparagraph a

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