Earnings Per Share - Earnings Per Share (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share [Abstract]
Income (loss) from continuing operations	$ (530)	$ 452	$ (80)	$ 933
Income from discontinued operations	0	77	0	103
Basic and diluted income (loss) available to common shareholders	$ 530	$ (529)	$ 80	$ (1,036)
Weighted Average Shares Outstanding
Basic weighted average shares outstanding	648.2	654.4	648.0	657.9
Effect of dilutive securities:
Stock options and unvested restricted stock	0.0	6.8	0.0	6.8
Diluted weighted average shares outstanding	648.2	661.2	648.0	664.7
Antidilutive Securities
Options to purchase common shares	0.0	0.5	0.0	0.4