Shareholders' Equity - Changes in Certain Components of Shareholders' Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended						9 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2019	Jun. 30, 2018
Dividends per Common Share (USD per share)	$ 0.77	$ 0.77	$ 0.77	$ 0.75	$ 0.75	$ 0.75	$ 2.31	$ 2.25
Beginning balance			$ 20,994				$ 20,994
Net income	$ 451			$ 594			1,071	$ 446
Ending balance	21,497						21,497
Common Stock Issued at Par Value
Beginning balance	347	$ 347	347	347	$ 347	$ 347	347	347
Ending balance	347	347	347	347	347	347	347	347
Capital in Excess of Par Value
Beginning balance	16,177	16,174	16,179	16,170	16,197	9,619	16,179	9,619
Common stock issued for acquisition					(9)	6,487
Common stock issued for share-based compensation and other plans, net	(6)	(57)	(97)	(25)	(94)	(51)
Share-based compensation	56	60	92	48	76	142
Ending balance	16,227	16,177	16,174	16,193	16,170	16,197	16,227	16,193
Retained Earnings
Beginning balance	12,792	13,018	12,596	12,616	12,765	13,111	12,596	13,111
Net income	451	20	599	594	(12)	(136)
Common dividends	(208)	(208)	(207)	(201)	(201)	(172)
Preferred dividends	(38)	(38)	(38)	(38)	(38)	(38)
Common stock issued for share-based compensation and other plans, net		(1)		(1)	(1)
Effect of changes in accounting principles (see Note 2)			68		103
Ending balance	12,997	12,792	13,018	12,971	12,616	12,765	12,997	12,971
Deferred Compensation
Beginning balance	23	24	22	21	19	19	22	19
Common stock issued for share-based compensation and other plans, net		(1)	2	1	2
Ending balance	23	23	24	22	21	19	23	22
Treasury Stock
Beginning balance	$ (6,192)	$ (6,235)	$ (6,243)	$ (6,300)	$ (6,343)	$ (8,427)	$ (6,243)	$ (8,427)
Beginning balance (shares)	(76,955)	(77,624)	(78,463)	(79,485)	(80,445)	(118,745)	(78,463)	(118,745)
Common stock issued for acquisition						$ 2,121
Common stock issued for acquisition (in shares)						37,306
Common stock issued for share-based compensation and other plans, net	$ (8)	$ 42	$ 9	$ 24	$ 44	$ (37)
Common stock issued for share-based compensation and other plans, net (in shares)	219	618	851	364	943	1,021
Common stock held in trusts, net	4	50	(12)	(2)	17	(27)
Ending balance	$ (6,201)	$ (6,192)	$ (6,235)	$ (6,275)	$ (6,300)	$ (6,343)	$ (6,201)	$ (6,275)
Ending balance (shares)	(76,733)	(76,955)	(77,624)	(79,124)	(79,485)	(80,445)	(76,733)	(79,124)