Stock-based compensation - Components of Stock-based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Components of stock-based compensation expense [Abstract]
Total stock-based compensation expense, pretax	$ 473	$ 401	$ 341
Tax benefit from stock-based compensation expense	(102)	(86)	(74)
Total stock-based compensation expense, net of tax	371	315	267
RSUs
Components of stock-based compensation expense [Abstract]
Total stock-based compensation expense, pretax	309	227	183
Performance units
Components of stock-based compensation expense [Abstract]
Total stock-based compensation expense, pretax	121	132	121
Stock options
Components of stock-based compensation expense [Abstract]
Total stock-based compensation expense, pretax	$ 43	$ 42	$ 37