Income Taxes - Effective Tax Rate Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Tax expense at Ireland statutory rate		$ 180	$ (54)	$ 0
State and local income taxes, net of federal benefit		(15)	(30)	(41)
Foreign tax rate differential		(6)	(127)	(109)
Notional interest deduction		(10)	(44)	(63)
Credits and incentives		(11)	(7)	(9)
Goodwill impairment	$ 2	0	9	0
Repatriation of foreign earnings		18	18	31
Foreign exchange		0	(1)	2
Impact of enacted tax rate changes		(26)	(3)	(5)
Audit settlements and change in uncertain tax positions		24	56	107
Change in valuation allowance		(85)	332	503
Impairment of subsidiaries		35	(24)	(3)
Tax impact of corporate equity transactions		133	(77)	0
Other		12	9	(3)
Income tax provision		$ 249	$ 57	$ 410

Effective Income Tax Rate Reconciliation, Impairment of Subsidiaries

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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