Loans and finance receivables (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Receivables [Abstract]
Loans and finance receivables before allowances and discounts	$ 21,685	$ 20,436
Allowances for uncollectible loans	(744)	(712)	$ (731)	$ (167)
Unamortized acquisition discounts and points	(544)	(523)
Loans and finance receivables	$ 20,397	$ 19,201

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Name:	us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant