Retirement and Post-Retirement Employee Benefit Plans - Schedule of Allocation of Plan Assets (Details) - Defined Benefit Plan	Sep. 30, 2018	Sep. 30, 2017
Domestic equities
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation	44.30%	43.90%
International equities
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation	15.40%	17.20%
Fixed income
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation	16.90%	10.60%
Company stock
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation	12.70%	11.80%
Other assets
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation	10.70%	16.50%
Minimum | Domestic equities
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	35.00%
Minimum | International equities
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	10.00%
Minimum | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	5.00%
Minimum | Company stock
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	0.00%
Minimum | Other assets
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	0.00%
Maximum | Domestic equities
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	55.00%
Maximum | International equities
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	20.00%
Maximum | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	30.00%
Maximum | Company stock
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	15.00%
Maximum | Other assets
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	20.00%