Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Schedule of Income Tax Information [Line Items]
Federal statutory rate	21.00%			35.00%
Net income tax expense (benefit), tax reform	$ (43)
Net income tax expense (benefit), tax reform, per diluted share	$ (0.07)
Income tax expense (benefit), continuing operations, adjustment of deferred tax (asset) liability	$ (98)
Income tax expense (benefit), repatriation of foreign earnings and withholding taxes	185
Income tax expense (benefit) for repatriation of foreign earnings, prior periods	$ (130)
Scenario, Forecast [Member]
Schedule of Income Tax Information [Line Items]
Effective income tax rate		25.00%
Scenario, Forecast [Member] | Minimum [Member]
Schedule of Income Tax Information [Line Items]
Effective income tax rate			25.00%
Scenario, Forecast [Member] | Maximum [Member]
Schedule of Income Tax Information [Line Items]
Effective income tax rate			27.00%