Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		12 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Net income		$ 10,301	$ 6,699	$ 5,991	[1]
Dilutive shares of outstanding stock awards included in computation of weighted-average dilutive shares outstanding		3	5	5
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		1	2	2
Class A common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	[1]	$ 7,937	$ 5,170	$ 4,738
Weighted Average Shares Outstanding - Basic		1,792	1,845	1,906
Earnings per Share - Basic		$ 4.43	$ 2.80	$ 2.49	[2]
Income allocation - Diluted	[1]	$ 10,301	$ 6,699	$ 5,991
Weighted Average Shares Outstanding - Diluted	[3]	2,329	2,395	2,414
Earnings per Share - Diluted	[2]	$ 4.42	$ 2.80	$ 2.48
Class B common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	[1]	$ 1,787	$ 1,134	$ 1,006
Weighted Average Shares Outstanding - Basic		245	245	245
Earnings per Share - Basic		$ 7.28	$ 4.62	$ 4.10	[2]
Income allocation - Diluted	[1]	$ 1,785	$ 1,132	$ 1,004
Weighted Average Shares Outstanding - Diluted		245	245	245
Earnings per Share - Diluted	[2]	$ 7.27	$ 4.61	$ 4.09
Weighted Average Number Shares Outstanding, As-Converted Basis		403	405	405
Class C common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	[1]	$ 218	$ 163	$ 185
Weighted Average Shares Outstanding - Basic		12	14	19
Earnings per Share - Basic		$ 17.72	$ 11.21	$ 9.94	[2]
Income allocation - Diluted	[1]	$ 217	$ 162	$ 185
Weighted Average Shares Outstanding - Diluted		12	14	19
Earnings per Share - Diluted	[2]	$ 17.69	$ 11.19	$ 9.93
Weighted Average Number Shares Outstanding, As-Converted Basis		49	58	75
Participating Securities
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	[1],[4]	$ 359	$ 232	$ 62
Income allocation - Diluted	[1],[4]	$ 358	$ 232	$ 61
Series B Preferred Stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Weighted Average Number Shares Outstanding, As-Converted Basis		32	33
Series C Preferred Stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Weighted Average Number Shares Outstanding, As-Converted Basis		44	44

[1] Net income is allocated based on proportional ownership on an as-converted basis. The weighted-average number of shares of as-converted class B common stock used in the income allocation was 403 million for fiscal 2018, and 405 million for fiscal 2017 and 2016. The weighted-average number of shares of as-converted class C common stock used in the income allocation was 49 million, 58 million and 75 million for fiscal 2018, 2017 and 2016, respectively. The weighted-average number of shares of preferred stock included within participating securities was 32 million and 33 million of as-converted UK&I preferred stock for fiscal 2018 and 2017, respectively, and 44 million of as-converted Europe preferred stock for fiscal 2018 and 2017.

[2] Figures in the table may not recalculate exactly due to rounding. Earnings per share is calculated based on unrounded numbers.

[3] Weighted-average diluted shares outstanding are calculated on an as-converted basis, and include incremental common stock equivalents, as calculated under the treasury stock method. The computation includes 3 million common stock equivalents for fiscal 2018, and 5 million common stock equivalents for fiscal 2017 and 2016, because their effect would have been dilutive. The computation excludes 1 million of common stock equivalents for fiscal 2018, and 2 million of common stock equivalents for fiscal 2017 and 2016, because their effect would have been anti-dilutive.

[4] Participating securities include preferred stock outstanding and unvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents, such as the Company’s UK&I and Europe preferred stock, restricted stock awards, restricted stock units and earned performance-based shares. Participating securities’ income is allocated based on the weighted-average number of shares of as-converted stock. See Note 11—Stockholders’ Equity.