Basic and Diluted Earnings Per Share (Parenthetical) (Detail) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Stock options included in the computation of diluted shares outstanding	2	3	2	3
Stock Options | Maximum
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Stock options excluded from computation of average dilutive shares outstanding	1	1	1	1
Class B common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Weighted-average as-converted class B common stock used in income allocation	103	104	103	112