Income taxes - Components of deferred income tax assets and liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Deferred income tax assets:
Stock-based compensation	$ 244	$ 229
Deferred loss and tax credit carryforwards	226	289
Accrued expenses	215	246
Inventories and related reserves	147	156
Retirement costs for defined benefit and retiree health care	87	80
Other	101	87
Total deferred income tax assets, before valuation allowance	1,020	1,087
Valuation allowance	(186)	(195)
Total deferred income tax assets, after valuation allowance	834	892
Deferred income tax liabilities:
Acquisition-related intangibles and fair-value adjustments	(565)	(672)
International earnings	(105)	(104)
Total deferred income tax liabilities	(670)	(776)
Net deferred income tax asset	$ 164	$ 116