Loans and finance receivables - Schedule of reconciliation of allowance for credit losses on loans and finance receivables (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Allowance For Credit Loss [Abstract]
Balance at beginning of year	$ 712	$ 167
Adoption of ASC 326		486
Provision for credit losses	27	86
Charge-offs, net of recoveries	(14)	(37)
Balance at March 31	$ 725	$ 702