Income Taxes Changes in Tax Legislation and Statutory Tax Rates (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018
Change in Tax Legislation and Statutory Tax Rates [Line Items]
Income tax provision	$ 108	$ 217	$ (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)