Employee benefit plans - Summarizes the other changes in plan assets and benefit obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension
Employee benefit plans
Net loss (gain)	$ 40	$ 25	$ 9
Amortization of net (loss) gain	(1)
Total recognized in other comprehensive loss (income)	39	25	9
Total recognized in net periodic benefit cost (credit) and other comprehensive loss (income)	35	24	3
Other Postretirement
Employee benefit plans
Net loss (gain)	4		(2)
Amortization of net (loss) gain		1	1
Total recognized in other comprehensive loss (income)	$ 4	1	(1)
Total recognized in net periodic benefit cost (credit) and other comprehensive loss (income)		$ 1	$ (1)