Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Net income	[1]	$ 2,522	$ 2,070
Class A common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	[1]	$ 1,945	$ 1,594
Weighted- Average Shares Outstanding - Basic		1,811	1,860
Earnings per Share - Basic	[2]	$ 1.07	$ 0.86
Income Allocation - Diluted	[1]	$ 2,522	$ 2,070
Weighted- Average Shares Outstanding - Diluted	[3]	2,353	2,421
Earnings per Share - Diluted	[2]	$ 1.07	$ 0.86
Class B common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	[1]	$ 435	$ 347
Weighted- Average Shares Outstanding - Basic		245	245
Earnings per Share - Basic	[2]	$ 1.77	$ 1.41
Income Allocation - Diluted	[1]	$ 434	$ 346
Weighted- Average Shares Outstanding - Diluted		245	245
Earnings per Share - Diluted	[2]	$ 1.77	$ 1.41
Class C common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	[1]	$ 54	$ 57
Weighted- Average Shares Outstanding - Basic		13	17
Earnings per Share - Basic	[2]	$ 4.30	$ 3.43
Income Allocation - Diluted	[1]	$ 54	$ 57
Weighted- Average Shares Outstanding - Diluted		13	17
Earnings per Share - Diluted	[2]	$ 4.29	$ 3.42
Participating securities
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	[1],[4]	$ 88	$ 72
Income Allocation - Diluted	[1],[4]	$ 87	$ 72

[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 405 million for the three months ended December 31, 2017 and 2016. The weighted-average number of shares of as-converted class C common stock used in the income allocation was 51 million and 67 million for the three months ended December 31, 2017 and 2016, respectively. The weighted-average number of shares of preferred stock, included within participating securities, was 32 million and 35 million of as-converted UK&I preferred stock for the three months ended December 31, 2017 and 2016, respectively, and 44 million of as-converted Europe preferred stock for the three months ended December 31, 2017 and 2016.

[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 5 million common stock equivalents for the three months ended December 31, 2017 and 2016, because their effect would be dilutive. The computation excludes 2 million and 3 million of common stock equivalents for the three months ended December 31, 2017 and 2016, 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.