Plan's Investments at Fair Value (Detail) (Fair Value, Measurements, Recurring, USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	$ 777	$ 321
Level 1 | Cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	26	79
Level 1 | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	751	242
Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	255	627
Level 2 | Collective investment funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	0	391
Level 2 | Corporate debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	106	115
Level 2 | Debt securities of U.S. treasury and federal agencies
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	149	121
Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	23	25
Level 3 | Asset-backed securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	23	25
Total
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	1,055	973
Total | Cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	26	79
Total | Collective investment funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	0	391
Total | Corporate debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	106	115
Total | Debt securities of U.S. treasury and federal agencies
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	149	121
Total | Asset-backed securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	23	25
Total | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements	$ 751	$ 242