Contingencies and Legal Proceedings Contingencies (Details) $ in Thousands	9 Months Ended
	Jun. 30, 2016 USD ($) Units reactors Insurance_layers Procedures Sites
Loss Contingencies
Nuclear liability insurance	$ 375,000
Assessment from licensees for each licensed reactor	$ 127,000
Number of licensed reactors in US | reactors	102
Nuclear accident assessment limitation per year per unit	$ 19,000
Number of licensed nuclear units | Units	7
Maximum assessment per nuclear incident	$ 891,000
Maximum payment required per incident in any one year	133,000
Total amount of protection available	$ 13,000,000
Surcharge for legal expenses	5.00%
Number of layers before Congress is required to take action | Insurance_layers	2
Amount of property, decommissioning, and decontamination insurance carried	$ 5,100,000
Amount of insurance available for loss at any one site	$ 2,100,000
Number of sites | Sites	1
Maximum amount of retrospecitve premiums	$ 132,000
Maximum indemnity if a covered accident takes or keeps a nuclear unit offline	490,000
Maximum retrospective premiums	$ 37,000
Number of procedures for determining estimates for the costs of nuclear decommissioning | Procedures	2
Possible additional future costs for compliance with Clean Air Act requirements	$ 420,000
Amount of settlement for potential liability related to soil cleanup	300
Amount of settlement for potential liability related to EPA study of site	8
Remaining cleanup, remediation, and natural resource damages are less than	1,000
Accrual for Environmental Loss Contingencies, Gross	23,000
Non-nuclear | Non-nuclear
Loss Contingencies
Present value of estimated future decommissioning cost	1,500,000
Nuclear | Nuclear
Loss Contingencies
Present value of estimated future decommissioning cost	$ 2,500,000