Earnings per share - Narrative (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive options outstanding (in shares)	7.5	7.0	7.9
Stock Option Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of options excluded from the computation of diluted earnings per share (in shares)	0.1	0.0	0.2