Revenue Recognition Contract balances (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Contract liabilities - current	$ (1,710)		$ (1,710)		$ (1,435)
Total contract balances, net	(479)		(479)		(181)
Contract with Customer, Liability, Revenue Recognized	221	$ 326	935	$ 1,012
Accounts Receivable [Member]
Disaggregation of Revenue [Line Items]
Contract assets - current	1,387		1,387		1,395
Other Noncurrent Assets
Disaggregation of Revenue [Line Items]
Contract assets - noncurrent	102		102		104
Deferred Revenue [Member]
Disaggregation of Revenue [Line Items]
Contract liabilities - current	(1,710)		(1,710)		(1,435)
Other Noncurrent Liabilities [Member]
Disaggregation of Revenue [Line Items]
Contract liabilities - noncurrent	$ (258)		$ (258)		$ (245)