Benefit Plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Postemployment benefit costs	$ 12	$ 12	$ 23	$ 23
Post-65 Group Medical Coverage [Member]
Defined Benefit Plan Disclosure [Line Items]
Description of plan amendment			Effective April 1, 2014, the Company replaced its current post-65 group medical coverage with a new approach for retirees age 65 and older and their eligible dependents to access post-65 retiree medical and prescription drug coverage in the U.S.