Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 16,289	$ 7,838	$ 8,162
Cash, cash equivalents, restricted cash and restricted cash equivalents	19,171	10,832	10,977	$ 12,011
U.S. litigation escrow
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and restricted cash equivalents	901	1,205	1,491
Customer collateral
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and restricted cash equivalents	1,850	1,648	1,324
Prepaid expenses and other current assets
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and restricted cash equivalents	$ 131	$ 141	$ 0