Guarantees Of Debt (Schedule Of Financial Statements Of Guarantors) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Debt Instrument [Line Items]
Operating Revenues	$ 2,263	$ 2,450	$ 6,988	$ 6,971
Operating Expenses	1,570	1,873	5,921	5,220
Operating Income (Loss)	693	577	1,067	1,751
Equity Earnings (Losses) of Subsidiaries	3	3	11	9
Other Income	66	47	208	139
Other Deductions	(10)	(8)	(30)	(39)
Other-Than-Temporary Impairments	(5)	(5)	(9)	(25)
Interest Expense	(100)	(99)	(289)	(288)
Income Tax Benefit (Expense)	(252)	(188)	(340)	(562)
Net Income (Loss)	395	327	618	985
Net Cash Provided By (Used In) Operating Activities			2,734	2,761
Net Cash Provided By (Used In) Investing Activities			(3,104)	(3,054)
Net Cash Provided By (Used In) Financing Activities			225	349
Current Assets	3,081		3,081		$ 3,254
Property, Plant and Equipment, net	30,533		30,533		29,286
Noncurrent Assets	7,543		7,543		7,530
Total Assets	41,157		41,157		40,070
Current Liabilities	3,831		3,831		3,276
Noncurrent Liabilities	12,928		12,928		12,769
Long-Term Debt	11,274		11,274		10,895
Member's Equity	13,124		13,124		13,130
TOTAL LIABILITIES AND CAPITALIZATION	41,157		41,157		40,070
Power [Member]
Debt Instrument [Line Items]
Operating Revenues	873	1,075	3,086	3,102
Operating Expenses	660	837	3,363	2,533
Operating Income (Loss)	213	238	(277)	569
Equity Earnings (Losses) of Subsidiaries	3	3	11	9
Other Income	43	23	127	74
Other Deductions	(8)	(6)	(22)	(33)
Other-Than-Temporary Impairments	(5)	(5)	(9)	(25)
Interest Expense	(12)	(24)	(41)	(66)
Income Tax Benefit (Expense)	(98)	(90)	80	(208)
Net Income (Loss)	136	139	(131)	320
Net Cash Provided By (Used In) Operating Activities			1,249	1,260
Net Cash Provided By (Used In) Investing Activities			(884)	(1,151)
Net Cash Provided By (Used In) Financing Activities			(354)	(109)
Current Assets	1,162		1,162		1,460
Property, Plant and Equipment, net	8,072		8,072		8,520
Noncurrent Assets	2,397		2,397		2,213
Total Assets	11,631		11,631		12,193
Current Liabilities	764		764		680
Noncurrent Liabilities	3,105		3,105		3,332
Long-Term Debt	2,385		2,385		2,382
Member's Equity	5,377		5,377		5,799
TOTAL LIABILITIES AND CAPITALIZATION	11,631		11,631		12,193
Power Senior Notes [Member] | Consolidating Adjustments [Member]
Debt Instrument [Line Items]
Operating Revenues	(29)	(27)	(95)	(90)
Operating Expenses	(29)	(27)	(95)	(90)
Operating Income (Loss)	0	0	0	0
Equity Earnings (Losses) of Subsidiaries	(140)	(142)	119	(346)
Other Income	(37)	(21)	(99)	(66)
Other Deductions	0	0	0	0
Other-Than-Temporary Impairments	0	0	0	0
Interest Expense	37	21	99	66
Income Tax Benefit (Expense)	0	0	0	0
Net Income (Loss)	(140)	(142)	119	(346)
Comprehensive Income (Loss)	(154)	(163)	75	(392)
Net Cash Provided By (Used In) Operating Activities			3	(410)
Net Cash Provided By (Used In) Investing Activities			(990)	1,152
Net Cash Provided By (Used In) Financing Activities			987	(742)
Current Assets	(4,433)		(4,433)		(4,697)
Property, Plant and Equipment, net	0		0		0
Investment in Subsidiaries	(4,506)		(4,506)		(4,593)
Noncurrent Assets	(114)		(114)		(100)
Total Assets	(9,053)		(9,053)		(9,390)
Current Liabilities	(4,433)		(4,433)		(4,697)
Noncurrent Liabilities	(114)		(114)		(100)
Long-Term Debt	0		0		0
Member's Equity	(4,506)		(4,506)		(4,593)
TOTAL LIABILITIES AND CAPITALIZATION	(9,053)		(9,053)		(9,390)
Power Senior Notes [Member] | Power Parent [Member]
Debt Instrument [Line Items]
Operating Revenues	0	0	0	0
Operating Expenses	2	(2)	4	10
Operating Income (Loss)	(2)	2	(4)	(10)
Equity Earnings (Losses) of Subsidiaries	143	143	(111)	347
Other Income	24	18	71	52
Other Deductions	0	(2)	(1)	(2)
Other-Than-Temporary Impairments	0	0	0	0
Interest Expense	(32)	(30)	(96)	(91)
Income Tax Benefit (Expense)	3	8	10	24
Net Income (Loss)	136	139	(131)	320
Comprehensive Income (Loss)	156	168	(72)	388
Net Cash Provided By (Used In) Operating Activities			(55)	175
Net Cash Provided By (Used In) Investing Activities			738	(588)
Net Cash Provided By (Used In) Financing Activities			(683)	413
Current Assets	4,089		4,089		4,412
Property, Plant and Equipment, net	57		57		55
Investment in Subsidiaries	4,168		4,168		4,249
Noncurrent Assets	184		184		168
Total Assets	8,498		8,498		8,884
Current Liabilities	233		233		171
Noncurrent Liabilities	503		503		532
Long-Term Debt	2,385		2,385		2,382
Member's Equity	5,377		5,377		5,799
TOTAL LIABILITIES AND CAPITALIZATION	8,498		8,498		8,884
Power Senior Notes [Member] | Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	856	1,059	3,036	3,061
Operating Expenses	643	826	3,315	2,494
Operating Income (Loss)	213	233	(279)	567
Equity Earnings (Losses) of Subsidiaries	(3)	(1)	(8)	(1)
Other Income	58	26	155	88
Other Deductions	(8)	(4)	(21)	(31)
Other-Than-Temporary Impairments	(5)	(5)	(9)	(25)
Interest Expense	(12)	(12)	(30)	(29)
Income Tax Benefit (Expense)	(103)	(97)	68	(234)
Net Income (Loss)	140	140	(124)	335
Comprehensive Income (Loss)	154	161	(80)	381
Net Cash Provided By (Used In) Operating Activities			1,159	1,261
Net Cash Provided By (Used In) Investing Activities			(289)	(1,166)
Net Cash Provided By (Used In) Financing Activities			(869)	(95)
Current Assets	1,324		1,324		1,593
Property, Plant and Equipment, net	5,408		5,408		6,145
Investment in Subsidiaries	338		338		344
Noncurrent Assets	2,211		2,211		2,016
Total Assets	9,281		9,281		10,098
Current Liabilities	3,221		3,221		3,752
Noncurrent Liabilities	2,192		2,192		2,398
Long-Term Debt	0		0		0
Member's Equity	3,868		3,868		3,948
TOTAL LIABILITIES AND CAPITALIZATION	9,281		9,281		10,098
Power Senior Notes [Member] | Non-Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	46	43	145	131
Operating Expenses	44	40	139	119
Operating Income (Loss)	2	3	6	12
Equity Earnings (Losses) of Subsidiaries	3	3	11	9
Other Income	(2)	0	0	0
Other Deductions	0	0	0	0
Other-Than-Temporary Impairments	0	0	0	0
Interest Expense	(5)	(3)	(14)	(12)
Income Tax Benefit (Expense)	2	(1)	2	2
Net Income (Loss)	0	2	5	11
Comprehensive Income (Loss)	0	2	5	11
Net Cash Provided By (Used In) Operating Activities			142	234
Net Cash Provided By (Used In) Investing Activities			(343)	(549)
Net Cash Provided By (Used In) Financing Activities			211	315
Current Assets	182		182		152
Property, Plant and Equipment, net	2,607		2,607		2,320
Investment in Subsidiaries	0		0		0
Noncurrent Assets	116		116		129
Total Assets	2,905		2,905		2,601
Current Liabilities	1,743		1,743		1,454
Noncurrent Liabilities	524		524		502
Long-Term Debt	0		0		0
Member's Equity	638		638		645
TOTAL LIABILITIES AND CAPITALIZATION	2,905		2,905		2,601
Power Senior Notes [Member] | Power [Member]
Debt Instrument [Line Items]
Operating Revenues	873	1,075	3,086	3,102
Operating Expenses	660	837	3,363	2,533
Operating Income (Loss)	213	238	(277)	569
Equity Earnings (Losses) of Subsidiaries	3	3	11	9
Other Income	43	23	127	74
Other Deductions	(8)	(6)	(22)	(33)
Other-Than-Temporary Impairments	(5)	(5)	(9)	(25)
Interest Expense	(12)	(24)	(41)	(66)
Income Tax Benefit (Expense)	(98)	(90)	80	(208)
Net Income (Loss)	136	139	(131)	320
Comprehensive Income (Loss)	156	$ 168	(72)	388
Net Cash Provided By (Used In) Operating Activities			1,249	1,260
Net Cash Provided By (Used In) Investing Activities			(884)	(1,151)
Net Cash Provided By (Used In) Financing Activities			(354)	$ (109)
Current Assets	1,162		1,162		1,460
Property, Plant and Equipment, net	8,072		8,072		8,520
Investment in Subsidiaries	0		0		0
Noncurrent Assets	2,397		2,397		2,213
Total Assets	11,631		11,631		12,193
Current Liabilities	764		764		680
Noncurrent Liabilities	3,105		3,105		3,332
Long-Term Debt	2,385		2,385		2,382
Member's Equity	5,377		5,377		5,799
TOTAL LIABILITIES AND CAPITALIZATION	$ 11,631		$ 11,631		$ 12,193