Sales and revenue recognition (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Jan. 01, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Trade receivables from dealers and end users	$ 6,821	$ 6,399
Long term trade receivables from dealers and end users	614	639
Long-term customer advances	424	$ 396
Revenue recognized from contract liability balance at beginning of period	617
Unsatisfied performance obligations with an original contract duration greater than one year	$ 5,500
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]: 2018-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Unsatisfied performance obligations with an original contract duration greater than one year	$ 2,400