Shareholders' Equity - Changes in Certain Components of Shareholders' Equity (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Jun. 01, 2023
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 25,282
Beginning balance (shares)	(81,283,191)
Net Income	$ 1,484	$ 1,779	$ 2,092
Stockholders' Equity Note, Spinoff Transaction		251
Ending balance	$ 25,796	$ 25,282
Ending balance (shares)	(80,202,608)	(81,283,191)
Common stock dividend per share (USD per share)	$ 3.64	$ 3.48	$ 3.32
Convertible Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred Stock, Shares Outstanding				1,500,000
Common Stock  Issued at Par Value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Convertible Preferred Stock, Shares Issued upon Conversion				5,955,000
Common Stock  Issued at Par Value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 365	$ 365	$ 365
Stock Issued During Period, Value, Conversion of Convertible Securities, Net of Adjustments	6
Ending balance	371	365	365
Capital in Excess of Par Value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	19,553	19,272	19,270
Stock Issued During Period, Value, Conversion of Convertible Securities, Net of Adjustments	(4)
Issuance of shares under employee and other plans, net	(88)	(108)	(85)
Share-based compensation	259	239	237
Treasury Stock, Value, Acquired, Cost Method		150	(150)
Ending balance	19,720	19,553	19,272
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	15,157	13,826	12,791
Net Income	1,484	1,779	2,092
Cash dividends, common	(1,046)	(992)	(958)
Dividends, Preferred Stock	(60)	(90)	(90)
Issuance of shares under employee and other plans, net		(1)
Stockholders' Equity Note, Spinoff Transaction		634
Ending balance	15,535	15,157	13,826
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other			(9)
Deferred Compensation
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	23	23	23
Issuance of shares under employee and other plans, net	1
Ending balance	24	23	23
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ (8,330)	$ (7,723)	$ (6,138)
Beginning balance (shares)	(81,283,000)	(80,164,000)	(74,623,000)
Issuance of shares under employee and other plans, net	$ 24	$ 44	$ 15
Share-based compensation plans, net (shares)	1,056,000	1,271,000	1,068,000
Common stock held in trusts, net (shares)	24,000	25,000	33,000
Treasury Stock, Value, Acquired, Cost Method		$ (650)	$ (1,600)
Treasury Stock, Shares, Acquired		(2,415,000)	(6,643,000)
Ending balance	$ (8,305)	$ (8,330)	$ (7,723)
Ending balance (shares)	(80,203,000)	(81,283,000)	(80,164,000)