Other assets - Non-Readily Marketable Equity Securities (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
Other Assets [Abstract]
Equity securities without readily determinable fair value, amount	$ 212			$ 212		$ 129
Equity securities without readily determinable fair value, upward price adjustment, annual amount	55	$ 6	$ 4	61	$ 10
Equity securities without readily determinable fair value, downward price adjustment, annual amount	0	0	0	0	0
Equity securities without readily determinable fair value, net adjustment, annual amount	55	$ 6	$ 4	61	$ 10
Equity securities without readily determinable fair value, upward price adjustment, cumulative amount amount	114			114
Equity securities without readily determinable fair value, downward price adjustment, cumulative amount	(4)			(4)
Equity securities without readily determinable fair value, net price adjustment, cumulative amount	$ 110			$ 110