Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2020	Mar. 31, 2019
Income Tax Contingency [Line Items]
Income tax provision (benefit)	$ 16		$ 64		$ 70	$ 74
Effective tax rate (as percent)	89.00%		(103.00%)		(100.00%)	(180.00%)
Foreign statutory income tax rate	12.50%		12.50%		12.50%	12.50%
Unrecognized tax benefits		$ 413
Unrecognized tax benefits that would impact effective tax rate		114
Net accrued interest		12
Interest and penalties accrued		2			$ 3
Restructuring costs					54
Non-cash impairment charges					0	$ 66
Fixed asset impairment charges			$ 66
Tax benefit from impairment charge			$ 2
Restructuring Charges
Income Tax Contingency [Line Items]
Income tax provision (benefit)					$ 1
YFAI
Income Tax Contingency [Line Items]
Income tax provision (benefit)		(4)
Non-cash impairment charges	$ 216	$ 216
GAAS
Income Tax Contingency [Line Items]
Statutory rate (as percent)			25.00%	15.00%
Income tax benefit, reduction of deferred tax liability			$ (7)