Income taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Contingency [Line Items]
Discrete tax benefits related to reinstatement of the U.S. R&D tax credit		$ 79,000,000
Discrete tax benefits related to U.S. benefit for manufacturing			252,000,000
Deferred tax asset, change in amount related to unutilized tax credits	24,000,000
Tax loss carryforward, U.S. and non-U.S.	108,000,000
Tax loss carryforward, U.S. and non-U.S., set to expire	0
Amount of undistributed foreign earnings	7,670,000,000
Cash payments for income taxes	1,104,000,000	569,000,000	171,000,000
Amount of deferred tax assets possibly to be realized	56,000,000	76,000,000
Unrecognized tax benefits	108,000,000	91,000,000	184,000,000	210,000,000
Audit Assessments Not Made
Income Tax Contingency [Line Items]
Unrecognized tax benefits	76,000,000
Change in Accounting Method Accounted for as Change in Estimate
Income Tax Contingency [Line Items]
Amount of unrecorded changes in unrecognized tax benefits	52,000,000
Audit Assessments
Income Tax Contingency [Line Items]
Unrecognized tax benefits	32,000,000
Increase Liability for Transfer Pricing Issues
Income Tax Contingency [Line Items]
Amount of unrecorded changes in unrecognized tax benefits	29,000,000
Settlement with Taxing Authority
Income Tax Contingency [Line Items]
Amount of unrecorded changes in unrecognized tax benefits	29,000,000
Foreign Tax Authority
Income Tax Contingency [Line Items]
Benefits from tax holidays	$ 44,000,000	$ 40,000,000	$ 51,000,000
Tax holiday, review time period	5 years