Financing Receivables - By Portfolio Segment (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($) item	Dec. 31, 2020 USD ($) item
Financing receivables
Number of classes of financing receivable | item	3	3
Amortized Cost	$ 12,413	$ 18,242
Allowance for credit losses:
Allowance for credit losses, beginning balance	263
Allowance for credit losses, ending balance	207	263
Client Financing Receivables
Financing receivables
Amortized Cost	11,687	15,822
Allowance for credit losses:
Allowance for credit losses, beginning balance	255	252
Write-offs	(14)	(34)
Recoveries	1	3
Additions/(releases)	(36)	34
Other	(5)	1
Allowance for credit losses, ending balance	201	255
Client Financing Receivables | Americas
Financing receivables
Amortized Cost	5,966	7,758
Allowance for credit losses:
Allowance for credit losses, beginning balance	141	142
Write-offs	(6)	(28)
Recoveries		0
Additions/(releases)	(20)	33
Other	(2)	(6)
Allowance for credit losses, ending balance	113	141
Client Financing Receivables | EMEA
Financing receivables
Amortized Cost	3,616	5,023
Allowance for credit losses:
Allowance for credit losses, beginning balance	77	69
Write-offs	(1)	(3)
Recoveries		0
Additions/(releases)	(10)	5
Other	(3)	6
Allowance for credit losses, ending balance	64	77
Client Financing Receivables | Asia Pacific
Financing receivables
Amortized Cost	2,105	3,042
Allowance for credit losses:
Allowance for credit losses, beginning balance	37	41
Write-offs	(7)	(3)
Recoveries	1	2
Additions/(releases)	(6)	(4)
Other	0	1
Allowance for credit losses, ending balance	$ 24	$ 37