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Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Income Tax Contingency [Line Items]
Goodwill impairment - Note G	$ 530	$ 0	$ 530	$ 0
Decrease in Unrecognized Tax Benefits is Reasonably Possible	1		1
Increase in Unrecognized Tax Benefits is Reasonably Possible	$ 3		$ 3
Current Fiscal Year [Member]
Income Tax Contingency [Line Items]
Effective tax rate (in hundredths)	2.00%		6.00%
Nondeductible goodwill impairment	$ 527
Prior Fiscal Year [Member]
Income Tax Contingency [Line Items]
Effective tax rate (in hundredths)		2.00%		(2500.00%)
Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount		$ 11		$ (30)