CONSOLIDATED STATEMENTS OF CHANGES IN PROPRIETARY CAPITAL (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Mar. 31, 2016	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2014
Power Program Appropriation Investment	$ 258		$ 258			$ 258
Power Program Retained Earnings	6,932		6,932			6,357
Nonpower Programs Appropriation Investment, Net	583		583			590
Accumulated Other Comprehensive Income (Loss) from Net Gains (Losses) on Cash Flow Hedges	(37)		(37)			(2)
Total Proprietary Capital	7,736	$ 6,727	7,736	$ 6,727	$ 7,473	7,203	$ 6,687	$ 6,104
Net income (loss)	291	32	572	609
Total other comprehensive income (loss)	(27)	9	(35)	19
Return on power program appropriation investment	(1)	(1)	(4)	(5)
Power Program Appropriation Investment
Power Program Appropriation Investment	258	258	258	258	258	258	258	258
Net income (loss)	0	0	0	0
Total other comprehensive income (loss)	0	0	0	0
Return on power program appropriation investment	0	0	0	0
Power Program Retained Earnings
Power Program Retained Earnings	6,932	5,852	6,932	5,852	6,640	6,357	5,819	5,240
Net income (loss)	293	34	579	617
Total other comprehensive income (loss)	0	0	0	0
Return on power program appropriation investment	(1)	(1)	(4)	(5)
Nonpower Programs Appropriation Investment, Net
Nonpower Programs Appropriation Investment, Net	583	593	583	593	585	590	595	601
Net income (loss)	(2)	(2)	(7)	(8)
Total other comprehensive income (loss)	0	0	0	0
Return on power program appropriation investment	0	0	0	0
Accumulated Other Comprehensive Income (Loss) from Net Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) from Net Gains (Losses) on Cash Flow Hedges	(37)	24	(37)	24	$ (10)	$ (2)	$ 15	$ 5
Net income (loss)	0	0	0	0
Total other comprehensive income (loss)	(27)	9	(35)	19
Return on power program appropriation investment	$ 0	$ 0	$ 0	$ 0