Income taxes - Provision for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Taxes calculated using the estimated annual effective tax rate	$ 337	$ 231	$ 934	$ 561
Discrete tax items	(9)	3	(109)	(378)
Provision for income taxes	$ 328	$ 234	$ 825	$ 183
Effective tax rate	14.00%	15.00%	13.00%	4.00%