Income taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 219	$ 241	$ 213	$ 681	$ 694
Effective tax rate	18.80%	19.00%	18.40%
Tax reserves	$ 120			120		$ 119
Impact on effective tax rate if tax reserves were unnecessary	120			120
Accrued interest, related to income taxes in the balance sheet	33			33
Additional tax expense related to interest				6	$ 5
Reasonably possible decrease in uncertain tax positions within the next 12 months, if a re-evaluation is required	$ 1			$ 1