Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalent (Details) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 7,838	$ 8,162	$ 9,874
Cash, cash equivalents, restricted cash and restricted cash equivalents	10,832	10,977	12,011	$ 7,647
U.S. litigation escrow
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and restricted cash equivalents	1,205	1,491	1,031
Customer collateral
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and restricted cash equivalents	1,648	1,324	1,106
Prepaid expenses and other current assets
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and restricted cash equivalents	$ 141	$ 0	$ 0