Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2018
Income Tax Contingency [Line Items]
Income tax provision (benefit)	$ 54	$ 10
Foreign statutory income tax rate	12.50%
Effective tax rate (as percent)		48.00%
Unrecognized tax benefits	$ 425
Unrecognized tax benefits that would impact effective tax rate	125
Net accrued interest	11
Income tax penalties and interest accrued	1
YFAI
Income Tax Contingency [Line Items]
Income tax provision (benefit)	(4)
Asset Impairment Charges	$ 216
GAAS
Income Tax Contingency [Line Items]
Statutory rate (as percent)		25.00%	15.00%
Income tax benefit, reduction of deferred tax liability		$ (7)