Income Tax - Additional Information (Detail) - USD ($)		3 Months Ended			6 Months Ended
	Jan. 01, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018
Income Taxes [Line Items]
Net discrete tax (benefits) charges related to tax settlements			$ (26,000,000)		$ (24,000,000)	$ 162,000,000
Net tax expense from impact of the Act			4,000,000		$ 17,000,000	189,000,000
Income tax rate	21.00%			35.00%
Percentage of dividend received deduction for foreign dividends					100.00%
(Provision) benefit for income taxes for deemed repatriation					$ 17,000,000
Uncertain tax positions from expirations of statute of limitations		$ 1,000,000			$ 8,000,000	$ 2,000,000
Earliest Tax Year [Member] | United States Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Tax years remain subject to examination					2014
Latest Tax Year [Member] | United States Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Tax years remain subject to examination					2017
State Tax Authorities [Member] | Earliest Tax Year [Member]
Income Taxes [Line Items]
Tax years remain subject to examination					2005
State Tax Authorities [Member] | Latest Tax Year [Member]
Income Taxes [Line Items]
Tax years remain subject to examination					2017
Non-U.S. Jurisdictions [Member] | Earliest Tax Year [Member]
Income Taxes [Line Items]
Tax years remain subject to examination					2002
Non-U.S. Jurisdictions [Member] | Latest Tax Year [Member]
Income Taxes [Line Items]
Tax years remain subject to examination					2017
Maximum [Member]
Income Taxes [Line Items]
Net discrete tax (benefits) charges related to tax settlements		$ 1,000,000
Uncertain tax positions from expirations of statute of limitations			$ 1,000,000