Other assets - Non-Readily Marketable Equity Securities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Other Assets [Abstract]
Equity securities without readily determinable fair value, amount	$ 101	$ 61
Equity securities without readily determinable fair value, upward price adjustment, annual amount	4	1	$ 0
Equity securities without readily determinable fair value, downward price adjustment, annual amount	0	(2)	0
Equity securities without readily determinable fair value, net adjustment, annual amount	4	$ (1)	$ 0
Equity securities without readily determinable fair value, upward price adjustment, cumulative amount amount	36
Equity securities without readily determinable fair value, downward price adjustment, cumulative amount	(4)
Equity securities without readily determinable fair value, net price adjustment, cumulative amount	$ 32