Income Taxes - Reconciliation Using U.S. Statutory Rate (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Computed tax expense at the federal statutory rate	$ (7)	$ 53	$ 29
Foreign impact of taxation at different rates, repatriation, valuation allowance, and other	4	17	(8)
Impact of the Tax Cuts and Jobs Act of 2017			159
Global Intangible Low Taxed Income (GILTI)	(4)	10
Impact of the Coronavirus Aid, Relief, and Economic Security ("CARES") Act of 2020	(10)
Impact of increase (decrease) in valuation allowance on U.S. deferred taxes	228
U.S. and state benefits from research and experimentation activities	(2)	(2)	(2)
Provision (settlement) of unrecognized tax benefits	(7)	(8)	1
Impact of goodwill impairment charge			18
Permanent differences, net		1	(1)
State taxes, net of federal effect	(11)	(1)	(3)
Provision (benefit) for income taxes	$ 191	$ 70	$ 193

Income tax reconciliation foreign impact of taxation at different rates repatriation valuation allowance and other.

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Income tax reconciliation global intangible low taxed income.

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Income tax reconciliation impact of coronavirus aid relief and economic security act.

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Income tax reconciliation nondeductible expense goodwill impairment losses.

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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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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax exempt income, equity in earnings (loss) of an unconsolidated subsidiary, minority noncontrolling interest income (loss), tax holiday, disposition of a business, disposition of an asset, repatriation of foreign earnings, repatriation of foreign earnings jobs creation act of 2004, increase (decrease) in enacted tax rate, prior year income taxes, increase (decrease) in deferred tax asset valuation allowance, and other adjustments.

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Amount of income tax expense (benefit) for remeasurement of deferred tax from change in tax rate pursuant to Tax Cuts and Jobs Act.

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