Income Taxes Changes in Tax Legislation and Statutory Tax Rates (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018
Change in Tax Legislation and Statutory Tax Rates [Line Items]
Income tax provision	$ 47	$ 36		$ 155	$ 253	$ (108)
Transition Tax on Deemed Repatriated Earnings [Member]
Change in Tax Legislation and Statutory Tax Rates [Line Items]
Income tax provision			$ 305			216
Remeasurement of U.S. deferred tax assets and liabilities [Member]
Change in Tax Legislation and Statutory Tax Rates [Line Items]
Income tax provision			$ (101)			$ (108)