Earnings Per Share - Earnings Per Share (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share [Abstract]
Basic income available to common shareholders	$ 148	$ 379	$ 502	$ 803
Interest expense, net of tax	0	0	0	1
Diluted income available to common shareholders	$ 148	$ 379	$ 502	$ 804
Weighted Average Shares Outstanding
Basic weighted average shares outstanding (in shares)	684.0	680.0	683.6	679.9
Effect of dilutive securities:
Stock options and unvested restricted stock (in shares)	5.4	6.2	4.4	5.9
Equity units (in shares)	0	3.7	0	3.7
Diluted weighted average shares outstanding (in shares)	689.4	689.9	688.0	689.5
Antidilutive Securities
Options to purchase common shares (in shares)	0.5	0.7	1.6	1.1