Shareholders' Equity - Changes in Certain Components of Shareholders' Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended				6 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2024	Mar. 31, 2023
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		$ 25,796			$ 25,796
Net income	$ 537		$ 460		818	$ 969
Ending balance	$ 25,647				$ 25,647
Dividends per Common Share (USD per share)	$ 0.95	$ 0.95	$ 0.91	$ 0.91	$ 1.90	$ 1.82
Common Stock  Issued at Par Value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 371	$ 371	$ 365	$ 365	$ 371	$ 365
Ending balance	371	371	365	365	371	365
Capital in Excess of Par Value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	19,741	19,720	19,590	19,553	19,720	19,553
Issuance of shares under employee and other plans, net	(5)	(62)	(7)	(52)
Share-based compensation	60	83	56	89
Ending balance	19,795	19,741	19,639	19,590	19,795	19,639
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	15,540	15,535	15,384	15,157	15,535	15,157
Net income	537	281	460	509
Common dividends	(275)	(275)	(259)	(259)
Preferred dividends			(23)	(23)
Ending balance	15,802	15,540	15,563	15,384	15,802	15,563
Deferred Compensation
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	24	24	24	23	24	23
Issuance of shares under employee and other plans, net	2
Ending balance	26	24	24	24	26	24
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ (8,828)	$ (8,305)	$ (8,333)	$ (8,330)	$ (8,305)	$ (8,330)
Beginning balance (shares)	(81,692)	(80,203)	(80,738)	(81,283)	(80,203)	(81,283)
Issuance of shares under employee and other plans, net	$ 17	$ (20)	$ 5	$ (3)
Common stock issued for share-based compensation and other plans, net (in shares)	72	647	21	556
Common stock held in trusts, net (in shares)	32	(19)	92	(11)
Repurchase of common stock		$ (503)
Repurchase of common stock (in shares)		(2,118)
Ending balance	$ (8,811)	$ (8,828)	$ (8,327)	$ (8,333)	$ (8,811)	$ (8,327)
Ending balance (shares)	(81,588)	(81,692)	(80,625)	(80,738)	(81,588)	(80,625)