Benefit Plans - Net Pension and Postretirement Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 20,943	$ 23,029
Interest cost	21,684	27,989
Expected return on plan assets	(29,084)	(31,772)
Amortization of prior service credit	(3,260)	(3,370)
Amortization of loss	18,731	17,196
Net pension and postretirement cost	29,014	33,072
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,443	1,470
Interest cost	2,518	3,215
Expected return on plan assets
Amortization of prior service credit	(285)	(173)
Amortization of loss	977	1,162
Net pension and postretirement cost	$ 4,653	$ 5,674