Asset Retirement Obligations (Details) - Jun. 30, 2015 - USD ($) $ in Millions		Total
Asset Retirement Obligations
Asset retirement obligations, period increase (decrease)		$ 687
Decommissioning study update - ARO nuclear		5 years
Accretion expense		$ 33
Balance at September 30, 2014	[1]	3,169
Settlements (ash storage areas)	[1]	(33)
Additional obligations		606
Accretion (recorded as regulatory asset)	[1]	114
Balance at June 30, 2015	[1]	3,856
Current portion of ARO		180
Nuclear
Asset Retirement Obligations
Balance at September 30, 2014	[1]	2,052
Settlements (ash storage areas)	[1]	0
Additional obligations	[1]	0
Accretion (recorded as regulatory asset)	[1]	74
Balance at June 30, 2015	[1]	2,126
Non-nuclear
Asset Retirement Obligations
Balance at September 30, 2014	[1]	1,117
Settlements (ash storage areas)	[1]	(33)
Additional obligations		606
Accretion (recorded as regulatory asset)	[1]	40
Balance at June 30, 2015	[1]	1,730
EPA Ruling | Non-nuclear
Asset Retirement Obligations
Additional obligations		539
Coal-fired obligations | Non-nuclear
Asset Retirement Obligations
Additional obligations		60
Plant acquisition | Non-nuclear
Asset Retirement Obligations
Additional obligations		$ 7

[1] The current portion of ARO in the amount of $180 million is included in Accounts payable and accrued liabilities at June 30, 2015.