Income taxes - Provision for income taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
U.S. federal - Current	$ 357	$ 483	$ 979
Non-U.S. - Current	192	135	225
U.S. state - Current	10	12	7
Total current income tax expense (benefit)	559	630	1,211
U.S. federal - Deferred	(122)	25	(98)
Non-U.S. - Deferred	(15)	56	(8)
U.S. state - Deferred	0	0	1
Total deferred income tax expense (benefit)	(137)	81	(105)
Total U.S. federal income taxes	235	508	881
Total Non-U.S. income taxes	177	191	217
Total U.S. state income taxes	10	12	8
Provision for income taxes	$ 422	$ 711	$ 1,106