Income taxes (Details 6) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Operating loss and Tax credit carryforwards
Valuation allowance for deferred tax assets	$ 915	$ 993
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	$ 500
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	$ 1,804
Valuation allowance for deferred tax assets	192
U.S. state taxing jurisdictions | Expiration date next one to fifteen years
Operating loss and Tax credit carryforwards
Tax credit carryforwards	134
Non-U.S. taxing jurisdictions
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	4,489
Valuation allowance for deferred tax assets	723
Non-U.S. taxing jurisdictions | Expiring in 2019
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	23
Non-U.S. taxing jurisdictions | Expiring in 2020
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	124
Non-U.S. taxing jurisdictions | Expiring in 2021
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	92
Non-U.S. taxing jurisdictions | Expire between 2022-2024
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	147
Non-U.S. taxing jurisdictions | Expire between 2025-2039
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	506
Non-U.S. taxing jurisdictions | Unlimited
Operating loss and Tax credit carryforwards
Net operating loss carryforwards	$ 3,597