Basic and Diluted Earnings Per Share - Additional Information (Detail) - shares shares in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 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
Common stock equivalents excluded from computation of average dilutive shares outstanding	3	1
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
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	67	78
Series B Preferred Stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Weighted-average as-converted common stock used in income allocation	35
Series C Preferred Stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Weighted-average as-converted common stock used in income allocation	44