Income taxes (Details 4) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Noncurrent deferred and refundable income taxes	$ 1,363	$ 1,569
Deferred tax liabilities
Other liabilities	331	281
Deferred income taxes-net	$ 1,032	$ 1,288