Loans and finance receivables - Schedule of reconciliation of allowance for credit losses on loans and finance receivables (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Allowance For Credit Loss [Abstract]
Balance at beginning of year	$ 712	$ 167
Adoption of ASC 326		486
Provision for credit losses	49	130
Charge-offs, net of recoveries	(22)	(51)
Balance at June 30	$ 739	$ 732