Shareholders' Equity - Changes in Certain Components of Shareholders' Equity (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 23,765
Beginning balance (shares)	(74,622,657)
Net Income	$ 2,092	$ 874	$ 1,233
Ending balance	$ 23,677	$ 23,765
Ending balance (shares)	(80,163,949)	(74,622,657)
Common Stock  Issued at Par Value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 365	$ 347	347
Stock Issued During Period, Value, Conversion of Convertible Securities, Net of Adjustments		12
Stock Issued During Period, Value, New Issues		6
Ending balance	365	365	347
Capital in Excess of Par Value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	19,270	16,270	16,179
Common stock issued for share-based compensation and other plans, net	(85)	(143)	(170)
Share-based compensation	237	244	261
Stock Issued During Period, Value, Conversion of Convertible Securities, Net of Adjustments		(9)
Stock Issued During Period, Value, New Issues		2,909
Treasury Stock, Value, Acquired, Cost Method	(150)
Ending balance	19,272	19,270	16,270
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	12,791	12,913	12,596
Net Income	2,092	874	1,233
Cash dividends, common	(958)	(888)	(832)
Dividends, Preferred Stock	(90)	(107)	(152)
Common stock issued for share-based compensation and other plans, net			(1)
Ending balance	13,826	12,791	12,913
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other	(9)		68
Deferred Compensation
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	23	23	22
Common stock issued for share-based compensation and other plans, net			1
Ending balance	23	23	23
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ (6,138)	$ (6,190)	$ (6,243)
Beginning balance (shares)	(74,623,000)	(76,260,000)	(78,463,000)
Common stock issued for share-based compensation and other plans, net	$ 15	$ 52	$ 53
Share-based compensation plans, net (shares)	1,068,000	1,597,000	2,155,000
Common stock held in trusts, net (shares)	33,000	41,000	48,000
Treasury Stock, Value, Acquired, Cost Method	$ (1,600)
Treasury Stock, Shares, Acquired	(6,643,000)
Ending balance	$ (7,723)	$ (6,138)	$ (6,190)
Ending balance (shares)	(80,164,000)	(74,623,000)	(76,260,000)