Employee benefit plans - Summarizes the other changes in plan assets and benefit obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension
Employee benefit plans
Net loss (gain)	$ 25	$ 9	$ 5
Total recognized in other comprehensive loss (income)	25	9	5
Total recognized in net periodic benefit cost (credit) and other comprehensive loss (income)	24	3	4
Other Postretirement
Employee benefit plans
Net loss (gain)		(2)	(1)
Amortization of prior service (cost) credit			2
Amortization of net (loss) gain	1	1	1
Curtailment loss			1
Total recognized in other comprehensive loss (income)	1	(1)	3
Total recognized in net periodic benefit cost (credit) and other comprehensive loss (income)	$ 1	$ (1)	$ (24)