Revenue Recognition Contract balances (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Contract with Customer, Liability, Current	$ (1,600)		$ (1,600)		$ (1,407)
Contract with Customer Asset Liability Net	(202)		(202)		(45)
Contract with Customer, Liability, Revenue Recognized	326	$ 214	1,012	$ 926
Revenue, Remaining Performance Obligation, Amount	$ 14,400		$ 14,400
Remaining Performance Obligations Expected as Revenue Over the Next Two Years	60.00%		60.00%
Accounts Receivable [Member]
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, Net, Current	$ 1,422		$ 1,422		1,389
Other Noncurrent Assets
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, Net, Noncurrent	95		95		90
Other Noncurrent Liabilities [Member]
Disaggregation of Revenue [Line Items]
Contract with Customer, Liability, Noncurrent	(119)		(119)		(117)
Deferred Revenue [Member]
Disaggregation of Revenue [Line Items]
Contract with Customer, Liability, Current	$ (1,600)		$ (1,600)		$ (1,407)