Other assets - Non-Readily Marketable Equity Securities (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Other Assets [Abstract]
Equity securities without readily determinable fair value, amount	$ 106			$ 106		$ 61
Equity securities without readily determinable fair value, upward price adjustment, annual amount	2	$ 4	$ 2	6	$ 2
Equity securities without readily determinable fair value, downward price adjustment, annual amount	0	0	(1)	0	(1)
Equity securities without readily determinable fair value, net adjustment, annual amount	2	$ 4	$ 1	6	$ 1
Equity securities without readily determinable fair value, upward price adjustment, cumulative amount amount	38			38
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	$ 34			$ 34