Derivative Instruments and Hedging Activities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2020	Mar. 31, 2020	Sep. 30, 2019
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Reclassification of terminated interest rate swaps to interest expense within the next 12 months	$ (6)	$ (6)
Debt | Net Investment Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	1,400	1,400	$ 1,400
Foreign Exchange Contract
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	1,200	1,200	2,300
Currency Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	3,000	3,000	2,300
Fixed to Floating | Fair Value Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	375	375
Interest Rate Swap | Cash Flow Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	1,500	1,500	$ 1,500
Unrealized Gain (Loss) on Cash Flow Hedging Instruments	(111)	(74)
Commodity Contract | Cash Flow Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	$ 0	$ 0