Guarantees Of Debt (Schedule Of Financial Statements Of Guarantors) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Debt Instrument [Line Items]
Operating Revenues	$ 2,450	$ 2,688	$ 6,971	$ 8,137
Operating Expenses	1,873	1,874	5,220	5,707
Operating Income (Loss)	577	814	1,751	2,430
Equity Earnings (Losses) of Subsidiaries	3	3	9	10
Other Income	47	47	139	171
Other Deductions	(8)	(14)	(39)	(36)
Other-Than-Temporary Impairments	(5)	(30)	(25)	(45)
Interest Expense	(99)	(96)	(288)	(291)
Income Tax Expense	(188)	(285)	(562)	(869)
Net Income	327	439	985	1,370
Net Cash Provided By (Used In) Operating Activities			2,761	3,228
Net Cash Provided By (Used In) Investing Activities			(3,054)	(2,841)
Net Cash Provided By (Used In) Financing Activities			349	(518)
Current Assets	3,209		3,209		$ 3,494
Property, Plant and Equipment, net	28,804		28,804		26,539
Noncurrent Assets	7,475		7,475		7,502
Total Assets	39,488		39,488		37,535
Current Liabilities	2,804		2,804		3,575
Noncurrent Liabilities	12,511		12,511		12,059
Long-Term Debt	10,697		10,697		8,834
Member's Equity	13,476		13,476		13,067
TOTAL LIABILITIES AND CAPITALIZATION	39,488		39,488		37,535
Power [Member]
Debt Instrument [Line Items]
Operating Revenues	1,075	1,096	3,102	3,846
Operating Expenses	837	705	2,533	2,643
Operating Income (Loss)	238	391	569	1,203
Equity Earnings (Losses) of Subsidiaries	3	3	9	11
Other Income	23	25	74	109
Other Deductions	(6)	(14)	(33)	(32)
Other-Than-Temporary Impairments	(5)	(30)	(25)	(45)
Interest Expense	(24)	(30)	(66)	(94)
Income Tax Expense	(90)	(139)	(208)	(445)
Net Income	139	206	320	707
Net Cash Provided By (Used In) Operating Activities			1,260	1,558
Net Cash Provided By (Used In) Investing Activities			(1,151)	(1,150)
Net Cash Provided By (Used In) Financing Activities			(109)	(402)
Current Assets	1,759		1,759		1,949
Property, Plant and Equipment, net	8,707		8,707		8,127
Noncurrent Assets	2,344		2,344		2,174
Total Assets	12,810		12,810		12,250
Current Liabilities	794		794		1,226
Noncurrent Liabilities	3,495		3,495		3,338
Long-Term Debt	2,381		2,381		1,684
Member's Equity	6,140		6,140		6,002
TOTAL LIABILITIES AND CAPITALIZATION	12,810		12,810		12,250
Power Senior Notes [Member] | Consolidating Adjustments [Member]
Debt Instrument [Line Items]
Operating Revenues	(27)	(25)	(90)	(109)
Operating Expenses	(27)	(25)	(90)	(109)
Operating Income (Loss)	0	0	0	0
Equity Earnings (Losses) of Subsidiaries	(142)	(218)	(346)	(751)
Other Income	(21)	(11)	(66)	(35)
Other Deductions	0	0	0	0
Other-Than-Temporary Impairments	0	0	0	0
Interest Expense	21	11	66	35
Income Tax Expense	0	0	0	0
Net Income	(142)	(218)	(346)	(751)
Comprehensive Income (Loss)	(163)	(189)	(392)	(713)
Net Cash Provided By (Used In) Operating Activities			(410)	(769)
Net Cash Provided By (Used In) Investing Activities			1,152	1,191
Net Cash Provided By (Used In) Financing Activities			(742)	(422)
Current Assets	(5,262)		(5,262)		(4,828)
Property, Plant and Equipment, net	0		0		0
Investment in Subsidiaries	(5,192)		(5,192)		(4,847)
Noncurrent Assets	(76)		(76)		(76)
Total Assets	(10,530)		(10,530)		(9,751)
Current Liabilities	(5,262)		(5,262)		(4,828)
Noncurrent Liabilities	(76)		(76)		(76)
Long-Term Debt	0		0		0
Member's Equity	(5,192)		(5,192)		(4,847)
TOTAL LIABILITIES AND CAPITALIZATION	(10,530)		(10,530)		(9,751)
Power Senior Notes [Member] | Power Parent [Member]
Debt Instrument [Line Items]
Operating Revenues	0	0	0	0
Operating Expenses	(2)	3	10	7
Operating Income (Loss)	2	(3)	(10)	(7)
Equity Earnings (Losses) of Subsidiaries	143	220	347	755
Other Income	18	10	52	33
Other Deductions	(2)	0	(2)	(1)
Other-Than-Temporary Impairments	0	0	0	0
Interest Expense	(30)	(28)	(91)	(90)
Income Tax Expense	8	7	24	17
Net Income	139	206	320	707
Comprehensive Income (Loss)	168	184	388	690
Net Cash Provided By (Used In) Operating Activities			175	435
Net Cash Provided By (Used In) Investing Activities			(588)	(656)
Net Cash Provided By (Used In) Financing Activities			413	221
Current Assets	4,889		4,889		4,501
Property, Plant and Equipment, net	57		57		83
Investment in Subsidiaries	4,709		4,709		4,501
Noncurrent Assets	157		157		155
Total Assets	9,812		9,812		9,240
Current Liabilities	818		818		1,112
Noncurrent Liabilities	473		473		442
Long-Term Debt	2,381		2,381		1,684
Member's Equity	6,140		6,140		6,002
TOTAL LIABILITIES AND CAPITALIZATION	9,812		9,812		9,240
Power Senior Notes [Member] | Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	1,059	1,084	3,061	3,811
Operating Expenses	826	692	2,494	2,610
Operating Income (Loss)	233	392	567	1,201
Equity Earnings (Losses) of Subsidiaries	(1)	(2)	(1)	(4)
Other Income	26	26	88	111
Other Deductions	(4)	(14)	(31)	(31)
Other-Than-Temporary Impairments	(5)	(30)	(25)	(45)
Interest Expense	(12)	(8)	(29)	(24)
Income Tax Expense	(97)	(148)	(234)	(463)
Net Income	140	216	335	745
Comprehensive Income (Loss)	161	187	381	707
Net Cash Provided By (Used In) Operating Activities			1,261	1,826
Net Cash Provided By (Used In) Investing Activities			(1,166)	(1,382)
Net Cash Provided By (Used In) Financing Activities			(95)	(446)
Current Assets	1,845		1,845		1,912
Property, Plant and Equipment, net	6,570		6,570		6,502
Investment in Subsidiaries	483		483		346
Noncurrent Assets	2,140		2,140		1,959
Total Assets	11,038		11,038		10,719
Current Liabilities	3,888		3,888		3,866
Noncurrent Liabilities	2,704		2,704		2,597
Long-Term Debt	0		0		0
Member's Equity	4,446		4,446		4,256
TOTAL LIABILITIES AND CAPITALIZATION	11,038		11,038		10,719
Power Senior Notes [Member] | Non-Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	43	37	131	144
Operating Expenses	40	35	119	135
Operating Income (Loss)	3	2	12	9
Equity Earnings (Losses) of Subsidiaries	3	3	9	11
Other Income	0	0	0	0
Other Deductions	0	0	0	0
Other-Than-Temporary Impairments	0	0	0	0
Interest Expense	(3)	(5)	(12)	(15)
Income Tax Expense	(1)	2	2	1
Net Income	2	2	11	6
Comprehensive Income (Loss)	2	2	11	6
Net Cash Provided By (Used In) Operating Activities			234	66
Net Cash Provided By (Used In) Investing Activities			(549)	(303)
Net Cash Provided By (Used In) Financing Activities			315	245
Current Assets	287		287		364
Property, Plant and Equipment, net	2,080		2,080		1,542
Investment in Subsidiaries	0		0		0
Noncurrent Assets	123		123		136
Total Assets	2,490		2,490		2,042
Current Liabilities	1,350		1,350		1,076
Noncurrent Liabilities	394		394		375
Long-Term Debt	0		0		0
Member's Equity	746		746		591
TOTAL LIABILITIES AND CAPITALIZATION	2,490		2,490		2,042
Power Senior Notes [Member] | Power [Member]
Debt Instrument [Line Items]
Operating Revenues	1,075	1,096	3,102	3,846
Operating Expenses	837	705	2,533	2,643
Operating Income (Loss)	238	391	569	1,203
Equity Earnings (Losses) of Subsidiaries	3	3	9	11
Other Income	23	25	74	109
Other Deductions	(6)	(14)	(33)	(32)
Other-Than-Temporary Impairments	(5)	(30)	(25)	(45)
Interest Expense	(24)	(30)	(66)	(94)
Income Tax Expense	(90)	(139)	(208)	(445)
Net Income	139	206	320	707
Comprehensive Income (Loss)	168	$ 184	388	690
Net Cash Provided By (Used In) Operating Activities			1,260	1,558
Net Cash Provided By (Used In) Investing Activities			(1,151)	(1,150)
Net Cash Provided By (Used In) Financing Activities			(109)	$ (402)
Current Assets	1,759		1,759		1,949
Property, Plant and Equipment, net	8,707		8,707		8,127
Investment in Subsidiaries	0		0		0
Noncurrent Assets	2,344		2,344		2,174
Total Assets	12,810		12,810		12,250
Current Liabilities	794		794		1,226
Noncurrent Liabilities	3,495		3,495		3,338
Long-Term Debt	2,381		2,381		1,684
Member's Equity	6,140		6,140		6,002
TOTAL LIABILITIES AND CAPITALIZATION	$ 12,810		$ 12,810		$ 12,250