Sales and revenue recognition (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Jan. 01, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Trade receivables from dealers and end users	$ 6,902	$ 6,902	$ 6,399
Long term trade receivables from dealers and end users	664	664	639
Long-term customer advances	432	432	$ 396
Revenue recognized from contract liability balance at beginning of period	145	1,124
Unsatisfied performance obligations with an original contract duration greater than one year	5,900	$ 5,900
Period after which Collection of Future Income is Considered as Not Probable		120 days
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Unsatisfied performance obligations with an original contract duration greater than one year	$ 2,700	$ 2,700