Income taxes - Components of deferred tax assets and liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Deferred loss and tax credit carryforwards	$ 256	$ 214
Accrued expenses	119	219
Stock compensation	107	220
Inventories and related reserves	93	145
Retirement costs for defined benefit and retiree health care	38	82
Other	9	81
Total deferred tax assets, before valuation allowance	622	961
Valuation allowance	(165)	(128)
Total deferred tax assets, after valuation allowance	457	833
Deferred tax liabilities:
Acquisition-related intangibles and fair-value adjustments	(207)	(460)
International earnings	(64)	(32)
Total deferred tax liabilities	(271)	(492)
Net deferred tax asset	$ 186	$ 341