Plan's Investments at Fair Value (Detail) (USD $) In Millions	Sep. 30, 2011	Sep. 30, 2010
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	$ 783	$ 780
Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	235	236
Level 1 | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	55	46
Level 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	180	190
Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	515	518
Level 2 | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value		1
Level 2 | Collective investment funds
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	289	307
Level 2 | Corporate Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	122	99
Level 2 | Debt securities of U.S. treasury and federal agencies
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	104	111
Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	33	26
Level 3 | Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	33	26
Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	55	47
Collective investment funds
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	289	307
Corporate Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	122	99
Debt securities of U.S. treasury and federal agencies
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	104	111
Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	33	26
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Plan's investments at fair value	$ 180	$ 190