Retirement Plan And Other Post-Retirement Benefits (Narrative) (Details) - USD ($)	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Defined Benefit Plan Disclosure [Line Items]
Decrease to accumulated other comprehensive income	$ 171,586,000	$ (169,919,000)	$ (27,105,000)
Expected future benefit payments in year one	62,400,000
Expected future benefit payments in year two	63,600,000
Expected future benefit payments in year three	64,300,000
Expected future benefit payments in year four	64,800,000
Expected future benefit payments in year five	65,600,000
Expected future benefit payments in five years thereafter	333,900,000
Effect of one percentage point increase on accumulated postretirement benefit obligation	70,700,000
Effect of one percentage point increase on service and interest cost components	3,000,000
Effect of one percentage point decrease on accumulated postretirement benefit obligation	57,900,000
Effect of one percentage point decrease on service and interest cost components	2,500,000
Benefit assets transferred	0	0
Benefit assets transferred in/out of Level 3	$ 0	$ 0
Ultimate health care trend rate	4.50%	4.50%	4.50%
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 32,095,000	$ 37,700,000	$ 39,955,000
Accumulated benefit obligation	1,039,408,000	968,984,000	940,068,000
Benefit obligation	$ 1,097,421,000	$ 1,026,190,000	$ 999,499,000	$ 946,305,000
Discount rate	3.60%	4.25%	4.25%
Rate of compensation increase	4.70%	4.75%	4.75%
Employer Contributions	$ 7,000,000	$ 36,200,000	$ 33,500,000
Expected long term rate of return on plan assets	7.25%	7.50%	8.00%
Retirement Plan [Member] | Actuarial Experience [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase (decrease) in benefit obligation	$ (2,200,000)
Retirement Plan [Member] | Discount Rate Change [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase (decrease) in benefit obligation	78,500,000		$ 53,700,000
Retirement Plan [Member] | Mortality Assumption Change [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase (decrease) in benefit obligation		$ 24,200,000
Other Post-Retirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	12,923,000	10,446,000	10,593,000
Benefit obligation	$ 526,138,000	$ 464,987,000	$ 465,583,000	$ 460,634,000
Discount rate	3.70%	4.50%	4.25%
Rate of compensation increase	4.70%	4.75%	4.75%
Employer Contributions	$ 2,839,000	$ 2,161,000	$ 2,115,000
Expected future benefit payments in year one	26,511,000
Expected future benefit payments in year two	27,775,000
Expected future benefit payments in year three	28,901,000
Expected future benefit payments in year four	29,996,000
Expected future benefit payments in year five	31,071,000
Expected future benefit payments in five years thereafter	$ 164,611,000
Expected long term rate of return on plan assets	6.75%	7.00%	8.00%
Other Post-Retirement Benefit Plans [Member] | Actuarial Experience [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase (decrease) in benefit obligation	$ 11,000,000	$ 12,800,000	$ (25,300,000)
Other Post-Retirement Benefit Plans [Member] | Discount Rate Change [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase (decrease) in benefit obligation	49,400,000	(14,300,000)	26,400,000
Non-Qualified Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	7,500,000	7,000,000	7,500,000
Accumulated benefit obligation	72,400,000	66,000,000	65,700,000
Benefit obligation	$ 91,700,000	$ 85,800,000	$ 85,500,000
Discount rate	2.80%	3.50%	3.50%
Rate of compensation increase	7.75%	7.75%	7.50%
VEBA Trusts And 401(h) Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer Contributions	$ 2,600,000
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.60%
Other Than Veba Trust And 401(h) Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer Contributions	$ 200,000
Non-Qualified Benefit Plans, Other Post-Retirement Benefit Plan And Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase in other regulatory assets	55,900,000
Decrease to accumulated other comprehensive income	$ 11,300,000
Equity Securities [Member] | Retirement Plan and Veba Trusts And 401H Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, minimum	40.00%
Target allocation, maximum	60.00%
Fixed Income Securities [Member] | Retirement Plan and Veba Trusts And 401H Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, minimum	40.00%
Target allocation, maximum	60.00%
Other Securities [Member] | Retirement Plan and Veba Trusts And 401H Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, minimum	0.00%
Target allocation, maximum	15.00%
Effective Fiscal 2017 [Member] | Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected long term rate of return on plan assets	7.00%
Effective Fiscal 2017 [Member] | Other Post-Retirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected long term rate of return on plan assets	6.50%
Minimum [Member] | Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	$ 15,000,000
Minimum [Member] | VEBA Trusts And 401(h) Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	3,000,000
Maximum [Member] | Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	20,000,000
Maximum [Member] | VEBA Trusts And 401(h) Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	5,000,000
Other Accruals And Current Liabilities [Member] | Non-Qualified Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	9,800,000	$ 4,500,000	$ 6,600,000
Non-Current [Member] | Non-Qualified Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	81,900,000	81,300,000	78,900,000
Retirement Savings Account [Member]
Defined Benefit Plan Disclosure [Line Items]
Costs Recognized	2,600,000	2,300,000	1,900,000
Tax-Deferred Savings Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Costs Recognized	$ 5,900,000	$ 5,800,000	$ 5,200,000