Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Reclassificatons (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Reclassifications
Reclassification from Long-Term Assets to Long-Term Debt	$ 80
Reclassification from Other Assets to Long-term Power Bonds	67
Reclassification from Other Assets to Long-Term VIE	13
Reclassification from Other, net to Settlements from Asset Retirement Obligations	$ (58)	$ (14)