Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2019	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Effective income tax rate reconciliation, percent	20.00%	17.00%			19.00%	20.00%
Federal statutory income tax rate, percent						24.50%
Effective Income Tax Rate Reconciliation, Tax Settlement, Amount			$ 80			$ 81
Tax cuts and jobs act of 2017 deferred tax liability, provisional income tax (expense) benefit				$ 1,100
Tax cuts and jobs act of 2017 transition tax accumulated foreign earnings, provisional income tax expense (benefit)				$ 1,100
Increase in unrecognized tax benefits	$ 241				$ 387
Effective income tax rate reconciliation Unrecognized Tax Benefits that would Favorably Impact Effective Tax Rate	51				134
Accrued interest related to uncertain tax positions	$ 19				$ 51