Income taxes - Income before income taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income before income taxes - U.S.	$ 5,210	$ 4,915	$ 5,672
Income before income taxes - Non-U.S.	807	813	1,014
Income before income taxes	$ 6,017	$ 5,728	$ 6,686