Shareholders' Equity - Changes in Certain Components of Shareholders' Equity (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				$ 7,633					$ 7,633
Beginning balance (shares)				(119,370,934)					(119,370,934)
Net Income	$ 327	$ (132)	$ 344	$ 562	$ 19	$ 390	$ 338	$ 229	$ 1,100	$ 976	$ 695
Repurchase of common stock (shares)				(1,300,000)
Repurchase of common stock				$ (220)
Ending balance	$ 12,948				$ 7,633				$ 12,948	$ 7,633
Ending balance (shares)	(118,744,758)				(119,370,934)				(118,744,758)	(119,370,934)
Common Stock Issued at Par Value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				333				333	$ 333	$ 333	333
Net Income									0	0	0
Stock Issued During Period, Value, New Issues									14
Ending balance	$ 347				$ 333				347	333	333
Capital in Excess of Par Value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				4,693				4,475	4,693	4,475	2,198
Net Income									0	0	0
Stock Issued During Period, Value, New Issues									4,810
Share-based compensation and other plans, net									(65)	27	30
Share-based compensation									180	191	164
Acquisitions											2,083
Ending balance	9,619				4,693				9,619	4,693	4,475
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				12,727				12,314	12,727	12,314	12,105
Net Income									1,100	976	695
Cash dividends, common									(645)	(562)	(485)
Dividends, Preferred Stock									(70)
Share-based compensation and other plans, net									(1)	(1)	(2)
Ending balance	13,111				12,727				13,111	12,727	12,314
Deferred Compensation
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				22				20	22	20	19
Net Income									0	0	0
Share-based compensation and other plans, net									(3)	2	1
Ending balance	19				22				19	22	20
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				$ (8,212)				$ (8,239)	$ (8,212)	$ (8,239)	$ (8,601)
Beginning balance (shares)				(119,371,000)				(121,967,000)	(119,371,000)	(121,967,000)	(140,770,000)
Share-based compensation and other plans, net									$ 6	$ 26	$ (6)
Share-based compensation plans, net (shares)									1,908,000	2,607,000	2,839,000
Common stock held in trusts, net (shares)									7,000	(11,000)	5,000
Repurchase of common stock (shares)									(1,289,000)
Repurchase of common stock									$ (220)
Acquisitions											$ 368
Number of shares issued, in acquisition (shares)											15,959,000
Ending balance	$ (8,427)				$ (8,212)				$ (8,427)	$ (8,212)	$ (8,239)
Ending balance (shares)	(118,745,000)				(119,371,000)				(118,745,000)	(119,371,000)	(121,967,000)