Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Net income		$ 2,977	$ 2,522
Class A common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	[1]	$ 2,290	$ 1,945
Weighted- Average Shares Outstanding - Basic		1,760	1,811
Earnings per Share - Basic	[2]	$ 1.30	$ 1.07
Income Allocation - Diluted	[1]	$ 2,977	$ 2,522
Weighted- Average Shares Outstanding - Diluted	[3]	2,291	2,353
Earnings per Share - Diluted	[2]	$ 1.30	$ 1.07
Class B common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	[1]	$ 521	$ 435
Weighted- Average Shares Outstanding - Basic		245	245
Earnings per Share - Basic	[2]	$ 2.12	$ 1.77
Income Allocation - Diluted	[1]	$ 520	$ 434
Weighted- Average Shares Outstanding - Diluted		245	245
Earnings per Share - Diluted	[2]	$ 2.12	$ 1.77
Class C common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	[1]	$ 61	$ 54
Weighted- Average Shares Outstanding - Basic		12	13
Earnings per Share - Basic	[2]	$ 5.20	$ 4.30
Income Allocation - Diluted	[1]	$ 61	$ 54
Weighted- Average Shares Outstanding - Diluted		12	13
Earnings per Share - Diluted	[2]	$ 5.20	$ 4.29
Participating securities
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	[1],[4]	$ 105	$ 88
Income Allocation - Diluted	[1],[4]	$ 105	$ 87

[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 400 million and 405 million for the three months ended December 31, 2018 and 2017, respectively. The weighted-average number of shares of as-converted class C common stock used in the income allocation was 47 million and 51 million for the three months ended December 31, 2018 and 2017, respectively. The weighted-average number of shares of preferred stock included within participating securities was 32 million of as-converted UK&I preferred stock for the three months ended December 31, 2018 and 2017, and 44 million of as-converted Europe preferred stock for the three months ended December 31, 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 approximately 3 million and 5 million common stock equivalents for the three months ended December 31, 2018 and 2017, respectively, because their effect would be dilutive. The computation excludes 1 million and 2 million of common stock equivalents for the three months ended December 31, 2018, and 2017 respectively, 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.