Shareholders' Equity - Changes in Certain Components of Shareholders' Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Dividends per Common Share (USD per share)	$ 0.79	$ 0.77
Beginning balance	$ 21,081
Net income	278	$ 599
Ending balance	21,202
Common Stock Issued at Par Value
Beginning balance	347	347
Ending balance	347	347
Capital in Excess of Par Value
Beginning balance	16,270	16,179
Common stock issued for share-based compensation and other plans, net	(32)	(97)
Share-based compensation	82	92
Ending balance	16,320	16,174
Retained Earnings
Beginning balance	12,913	12,596
Net income	278	599
Common dividends	(215)	(207)
Preferred dividends	(38)	(38)
Effect of changes in accounting principle		68
Ending balance	12,938	13,018
Deferred Compensation
Beginning balance	23	22
Common stock issued for share-based compensation and other plans, net	1	2
Ending balance	24	24
Treasury Stock
Beginning balance	$ (6,190)	$ (6,243)
Beginning balance (shares)	(76,260)	(78,463)
Common stock issued for share-based compensation and other plans, net	$ (38)	$ 9
Common stock issued for share-based compensation and other plans, net (in shares)	758	851
Common stock held in trusts, net	(12)	(12)
Ending balance	$ (6,228)	$ (6,235)
Ending balance (shares)	(75,514)	(77,624)