Income taxes (Details 5) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating loss and Tax credit carryforwards
Valuation allowance for deferred tax assets	$ 993	$ 1,102
U.S. state taxing jurisdictions
Operating loss and Tax credit carryforwards
Net operating loss carryforward expiration, years	20 years
State tax credit carryforward expiration date, years	15 years
U.S. state taxing jurisdictions | Primarily over the next 20 years
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	$ 1,437
Valuation allowance for deferred tax assets	269
U.S. state taxing jurisdictions | Expiration date next one to fifteen years
Operating loss and Tax credit carryforwards
Tax credit carryforwards	124
Non-U.S. taxing jurisdictions
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	4,488
Valuation allowance for deferred tax assets	724
Non-U.S. taxing jurisdictions | Expiring in 2018
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	23
Non-U.S. taxing jurisdictions | Expiring in 2019
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	133
Non-U.S. taxing jurisdictions | Expiring in 2020
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	212
Non-U.S. taxing jurisdictions | Expire between 2021-2023
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	272
Non-U.S. taxing jurisdictions | Expire between 2024-2038
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	223
Non-U.S. taxing jurisdictions | Unlimited
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	$ 3,625