Debt - Additional Information (Detail) - USD ($)	3 Months Ended				12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Short-term debt, weighted average interest rate	1.15%		0.20%		1.15%	0.20%
Aggregate annual maturities of long-term debt, 2022	$ 433,000,000				$ 433,000,000
Aggregate annual maturities of long-term debt, 2023	2,749,000,000				2,749,000,000
Aggregate annual maturities of long-term debt, 2024	1,559,000,000				1,559,000,000
Aggregate annual maturities of long-term debt, 2025	2,164,000,000				2,164,000,000
Aggregate annual maturities of long-term debt, 2026	1,053,000,000.000				1,053,000,000.000
Debt Instrument, Term						364 days
Letters Of Credit Issuable Under Credit Facility	100,000,000				100,000,000
Swingline Loans Issuable Under Credit Facility	100,000,000				100,000,000
Line Of Credit Facility Maximum Additional Principal Amount Commitments	500,000,000				500,000,000
Line of Credit Facility, Maximum Borrowing Capacity	3,250,000,000				3,250,000,000
Long-term Commercial Paper	0				0
Long-Term Debt	$ 17,110,000,000		$ 17,224,000,000		17,110,000,000	$ 17,224,000,000
Debt Instrument, Repurchase Amount			951,000,000			951,000,000
Extinguishment of Debt, Gain (Loss), Net of Tax			1,000,000		$ 178,000,000	8,000,000	$ 59,000,000
Notes 2.894% due June 6, 2022
Debt Instrument [Line Items]
Interest rate	2.894%				2.894%
Debt Instrument, Repurchased Face Amount	$ 1,535,000,000	$ 265,000,000			$ 1,535,000,000
Debt Instrument, Repurchase Amount	1,566,000,000	275,000,000			$ 1,566,000,000
Extinguishment of Debt, Gain (Loss), Net of Tax	$ 32,000,000	$ 10,000,000
3.300% Notes due March 1, 2023
Debt Instrument [Line Items]
Interest rate	3.30%				3.30%
Debt Instrument, Repurchased Face Amount	$ 294,000,000				$ 294,000,000
Long-Term Debt	0		295,000,000		0	295,000,000
Debt Instrument, Repurchase Amount	307,000,000				$ 307,000,000
Extinguishment of Debt, Gain (Loss), Net of Tax	12,000,000
Revolving Credit Facility due December 29, 2022
Debt Instrument [Line Items]
Debt Instrument, Term					5 years
Borrowings under credit facility	0		$ 0		$ 0	$ 0
Revolving Credit Facility due December 29, 2022 | Maximum
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 2,750,000,000				$ 2,750,000,000
Term Loan Facility
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity				$ 2,000,000,000
Repayments of Lines of Credit				$ 1,900,000,000