Sales and revenue recognition (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue from External Customer [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 5,700
Contract with Customer, Receivable, after Allowance for Credit Loss, Current	6,310	$ 7,648	$ 7,743
Contract with Customer, Receivable, after Allowance for Credit Loss, Noncurrent	657	693	674
Contract with Customer, Liability	1,526	1,654	$ 1,680
Contract with Customer, Liability, Revenue Recognized	$ 1,012	$ 1,171
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]: 2021-01-01
Revenue from External Customer [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 2,200
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months