Income Taxes (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended	9 Months Ended		12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Federal tax 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)
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)
Net income tax expense (benefit), tax reform final regulations on deemed repatriation		$ (13)
Reversal of one-time tax on deemed repatriation of accumulated foreign earnings, offset by unrecognized tax benefits		$ 100
Income taxes	$ 155		$ 49		$ 429	$ 327
Effective income tax rate	20.00%		6.00%		21.00%	17.00%
Income tax expense (benefit) from restructuring a foreign subsidiary	$ (21)
Income tax expense (benefit) from restructuring a foreign subsidiary, per diluted share	$ (0.03)
Favorable discrete items, percentage impact					3.00%