Basic and Diluted Earnings Per Share - Additional Information (Detail) - shares shares in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Common stock equivalents included in the computation of diluted shares outstanding	5	5	5	5
Common stock equivalents excluded from computation of average dilutive shares outstanding	1	1	2	2
Class B common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Weighted-average as-converted common stock used in income allocation	405	405	405	405
Class C common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Weighted-average as-converted common stock used in income allocation	73	78	76	82