Commitments and Contingencies (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended		6 Months Ended			6 Months Ended
	Mar. 31, 2013 Environmental Matters [Member]	Sep. 30, 2012 Environmental Matters [Member]	Mar. 31, 2012 Environmental Matters [Member] Maximum [Member]	Mar. 31, 2013 Respirator Liabilities [Member] Claim	Sep. 30, 2012 Respirator Liabilities [Member] Claim	Mar. 31, 2012 Respirator Liabilities [Member] Maximum [Member]
Loss Contingencies [Line Items]
Reserve for environmental matters on discount	$ 6	$ 7
Reserve for environmental matters on undiscounted basis	6	7
Cash payments for environmental reserves	1		1	1		1
Number of claimants				42,000	42,000
Respirator reserve on discounted basis				12	13
Respirator reserve on undiscounted basis				$ 16	$ 17