Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2018	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)	$ (193)
Net income tax expense (benefit), tax reform, per diluted share		$ (0.07)	$ (0.30)
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)
Income tax expense (benefit) due to increase in foreign tax credit carryforwards	$ (150)
Income tax expense (benefit) due to increase in foreign tax credit carryforwards, per diluted share	$ (0.24)
Scenario, Forecast [Member]
Schedule of Income Tax Information [Line Items]
Effective income tax rate				25.00%	19.00%
Effective income tax rate, tax reform impact					7.00%