Shareholders' Equity - Changes in Certain Components of Shareholders' Equity (Details) - USD ($) shares in Thousands, $ in Millions	3 Months Ended						9 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	Jun. 30, 2019
Beginning balance			$ 21,081				$ 21,081
Net income	$ 286			$ 451			746	$ 1,071
Ending balance	24,022						24,022
Common Stock  Issued at Par Value
Beginning balance	347	$ 347	347	347	$ 347	$ 347	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	347	347	347	347	347	365	347
Capital in Excess of Par Value
Beginning balance	16,288	16,320	16,270	16,177	16,174	16,179	16,270	16,179
Common stock issued for share-based compensation and other plans, net	(12)	(91)	(32)	(6)	(57)	(97)
Share-based compensation	52	58	82	56	60	92
Stock Issued During Period, Value, Conversion of Convertible Securities, Net of Adjustments	(9)
Stock Issued During Period, Value, New Issues	2,909
Ending balance	19,228	16,288	16,320	16,227	16,177	16,174	19,228	16,227
Retained Earnings
Beginning balance	12,868	12,938	12,913	12,792	13,018	12,596	12,913	12,596
Net income		183	278	451	20	599
Common dividends	(229)	(215)	(215)	(208)	(208)	(207)
Preferred dividends	(9)	(38)	(38)	(38)	(38)	(38)
Common stock issued for share-based compensation and other plans, net					(1)
Stockholders' Equity, Other						68
Ending balance	12,916	12,868	12,938	12,997	12,792	13,018	12,916	12,997
Deferred Compensation
Beginning balance	23	24	23	23	24	22	23	22
Common stock issued for share-based compensation and other plans, net		(1)	1		(1)	2
Ending balance	23	23	24	23	23	24	23	23
Treasury Stock
Beginning balance	$ (6,158)	$ (6,228)	$ (6,190)	$ (6,192)	$ (6,235)	$ (6,243)	$ (6,190)	$ (6,243)
Beginning balance (shares)	(74,911)	(75,514)	(76,260)	(76,955)	(77,624)	(78,463)	(76,260)	(78,463)
Common stock issued for share-based compensation and other plans, net	$ 13	$ 70	$ (38)	$ (8)	$ 42	$ 9
Common stock issued for share-based compensation and other plans, net (in shares)	127	573	758	219	618	851
Common stock held in trusts, net (in shares)	13	30	(12)	4	50	(12)
Ending balance	$ (6,145)	$ (6,158)	$ (6,228)	$ (6,201)	$ (6,192)	$ (6,235)	$ (6,145)	$ (6,201)
Ending balance (shares)	(74,771)	(74,911)	(75,514)	(76,733)	(76,955)	(77,624)	(74,771)	(76,733)