Guarantees Of Debt (Schedule Of Financial Statements Of Guarantors) (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Subsidiary or Equity Method Investee [Line Items]
Operating Revenues	$ 2,278	$ 2,688	$ 2,314	$ 3,135	$ 2,773	$ 2,641	$ 2,249	$ 3,223	$ 10,415	$ 10,886	$ 9,968
Operating Expenses									7,453	8,263	7,669
Operating Income (Loss)	532	814	568	1,048	807	746	365	705	2,962	2,623	2,299
Equity Earnings (Losses) of Subsidiaries									12	13	11
Other Income									254	290	213
Other Deductions									(102)	(61)	(54)
Other-than-Temporary-Impairments									(53)	(20)	(12)
Interest Expense									(393)	(389)	(402)
Income Tax Benefit (Expense)									(1,001)	(938)	(812)
Net Income									1,679	1,518	1,243
Net Cash Provided By (Used In) Operating Activities									3,919	3,160	3,158
Net Cash Provided By (Used In) Investing Activities									(3,942)	(2,892)	(2,801)
Net Cash Provided By (Used In) Financing Activities									15	(359)	(243)
Current Assets	3,494				4,119				3,494	4,119
Property, Plant and Equipment, net	26,539				23,589				26,539	23,589
Noncurrent Assets	7,502				7,579				7,502	7,579
Total Assets	37,535				35,287				37,535	35,287	32,480
Current Liabilities	3,575				3,478				3,575	3,478
Noncurrent Liabilities	12,059				11,408				12,059	11,408
Member's Equity	13,067				12,186				13,067	12,186	11,609	$ 10,781
TOTAL LIABILITIES AND CAPITALIZATION	37,535				35,287				37,535	35,287
Power [Member]
Subsidiary or Equity Method Investee [Line Items]
Operating Revenues	1,082	1,096	1,025	1,725	1,610	1,138	986	1,700	4,928	5,434	5,063
Operating Expenses									3,498	4,225	3,993
Operating Income (Loss)	227	$ 391	$ 228	$ 584	507	$ 353	$ 67	$ 282	1,430	1,209	1,070
Equity Earnings (Losses) of Subsidiaries									14	14	16
Other Income									169	222	154
Other Deductions									(72)	(52)	(49)
Other-than-Temporary-Impairments									(53)	(20)	(12)
Interest Expense									(121)	(122)	(116)
Income Tax Benefit (Expense)									(511)	(491)	(419)
Net Income									856	760	644
Net Cash Provided By (Used In) Operating Activities									1,706	1,425	1,347
Net Cash Provided By (Used In) Investing Activities									(1,001)	(524)	(861)
Net Cash Provided By (Used In) Financing Activities									(702)	(898)	(487)
Current Assets	1,949				2,359				1,949	2,359
Property, Plant and Equipment, net	8,127				7,515				8,127	7,515
Noncurrent Assets	2,174				2,163				2,174	2,163
Total Assets	12,250				12,037				12,250	12,037
Current Liabilities	1,226				1,184				1,226	1,184
Noncurrent Liabilities	3,338				3,061				3,338	3,061
Total Long-Term Debt	1,684				2,234				1,684	2,234
Member's Equity	6,002				5,558				6,002	5,558	5,858	$ 5,630
TOTAL LIABILITIES AND CAPITALIZATION	12,250				12,037				12,250	12,037
Power Senior Notes [Member]
Subsidiary or Equity Method Investee [Line Items]
Operating Revenues									4,928	5,434	5,063
Operating Expenses									3,498	4,225	3,993
Operating Income (Loss)									1,430	1,209	1,070
Equity Earnings (Losses) of Subsidiaries									14	14	16
Other Income									169	222	154
Other Deductions									(72)	(52)	(49)
Other-than-Temporary-Impairments									(53)	(20)	(12)
Interest Expense									(121)	(122)	(116)
Income Tax Benefit (Expense)									(511)	(491)	(419)
Net Income									856	760	644
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									844	595	909
Net Cash Provided By (Used In) Operating Activities									1,706	1,425	1,347
Net Cash Provided By (Used In) Investing Activities									(1,001)	(524)	(861)
Net Cash Provided By (Used In) Financing Activities									(702)	(898)	(487)
Current Assets	1,949				2,359				1,949	2,359
Property, Plant and Equipment, net	8,127				7,515				8,127	7,515
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0				0				0	0
Noncurrent Assets	2,174				2,163				2,174	2,163
Total Assets	12,250				12,037				12,250	12,037
Current Liabilities	1,226				1,184				1,226	1,184
Noncurrent Liabilities	3,338				3,061				3,338	3,061
Total Long-Term Debt	1,684				2,234				1,684	2,234
Member's Equity	6,002				5,558				6,002	5,558
TOTAL LIABILITIES AND CAPITALIZATION	12,250				12,037				12,250	12,037
Power Senior Notes [Member] | Guarantor Subsidiaries [Member]
Subsidiary or Equity Method Investee [Line Items]
Operating Revenues									4,883	5,390	5,022
Operating Expenses									3,451	4,175	3,945
Operating Income (Loss)									1,432	1,215	1,077
Equity Earnings (Losses) of Subsidiaries									(4)	(5)	(5)
Other Income									174	222	157
Other Deductions									(45)	(32)	(35)
Other-than-Temporary-Impairments									(53)	(20)	(12)
Interest Expense									(39)	(35)	(42)
Income Tax Benefit (Expense)									(574)	(558)	(474)
Net Income									891	787	666
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									855	768	713
Net Cash Provided By (Used In) Operating Activities									2,089	1,674	1,503
Net Cash Provided By (Used In) Investing Activities									(1,519)	(856)	(1,092)
Net Cash Provided By (Used In) Financing Activities									(571)	(818)	(412)
Current Assets	1,912				2,037				1,912	2,037
Property, Plant and Equipment, net	6,502				6,265				6,502	6,265
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	346				120				346	120
Noncurrent Assets	1,959				1,952				1,959	1,952
Total Assets	10,719				10,374				10,719	10,374
Current Liabilities	3,866				3,606				3,866	3,606
Noncurrent Liabilities	2,597				2,442				2,597	2,442
Total Long-Term Debt	0				0				0	0
Member's Equity	4,256				4,326				4,256	4,326
TOTAL LIABILITIES AND CAPITALIZATION	10,719				10,374				10,719	10,374
Power Senior Notes [Member] | Non-Guarantor Subsidiaries [Member]
Subsidiary or Equity Method Investee [Line Items]
Operating Revenues									179	153	190
Operating Expenses									169	143	174
Operating Income (Loss)									10	10	16
Equity Earnings (Losses) of Subsidiaries									14	14	16
Other Income									0	0	0
Other Deductions									0	0	0
Other-than-Temporary-Impairments									0	0	0
Interest Expense									(19)	(19)	(19)
Income Tax Benefit (Expense)									6	2	0
Net Income									11	7	13
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									11	7	11
Net Cash Provided By (Used In) Operating Activities									80	76	82
Net Cash Provided By (Used In) Investing Activities									(430)	(42)	(71)
Net Cash Provided By (Used In) Financing Activities									354	(32)	(11)
Current Assets	364				150				364	150
Property, Plant and Equipment, net	1,542				1,169				1,542	1,169
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0				0				0	0
Noncurrent Assets	136				137				136	137
Total Assets	2,042				1,456				2,042	1,456
Current Liabilities	1,076				786				1,076	786
Noncurrent Liabilities	375				360				375	360
Total Long-Term Debt	0				0				0	0
Member's Equity	591				310				591	310
TOTAL LIABILITIES AND CAPITALIZATION	2,042				1,456				2,042	1,456
Power Senior Notes [Member] | Consolidation, Eliminations [Member]
Subsidiary or Equity Method Investee [Line Items]
Operating Revenues									(134)	(109)	(149)
Operating Expenses									(134)	(109)	(149)
Operating Income (Loss)									0	0	0
Equity Earnings (Losses) of Subsidiaries									(902)	(794)	(679)
Other Income									(53)	(34)	(38)
Other Deductions									0	0	0
Other-than-Temporary-Impairments									0	0	0
Interest Expense									53	34	38
Income Tax Benefit (Expense)									0	0	0
Net Income									(902)	(794)	(679)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									(866)	(775)	(724)
Net Cash Provided By (Used In) Operating Activities									(1,034)	(902)	(526)
Net Cash Provided By (Used In) Investing Activities									1,314	226	697
Net Cash Provided By (Used In) Financing Activities									(280)	676	(171)
Current Assets	(4,828)				(4,091)				(4,828)	(4,091)
Property, Plant and Equipment, net	0				0				0	0
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	(4,847)				(4,636)				(4,847)	(4,636)
Noncurrent Assets	(76)				(195)				(76)	(195)
Total Assets	(9,751)				(8,922)				(9,751)	(8,922)
Current Liabilities	(4,828)				(4,091)				(4,828)	(4,091)
Noncurrent Liabilities	(76)				(195)				(76)	(195)
Total Long-Term Debt	0				0				0	0
Member's Equity	(4,847)				(4,636)				(4,847)	(4,636)
TOTAL LIABILITIES AND CAPITALIZATION	(9,751)				(8,922)				(9,751)	(8,922)
Power Senior Notes [Member] | Power Parent [Member]
Subsidiary or Equity Method Investee [Line Items]
Operating Revenues									0	0	0
Operating Expenses									12	16	23
Operating Income (Loss)									(12)	(16)	(23)
Equity Earnings (Losses) of Subsidiaries									906	799	684
Other Income									48	34	35
Other Deductions									(27)	(20)	(14)
Other-than-Temporary-Impairments									0	0	0
Interest Expense									(116)	(102)	(93)
Income Tax Benefit (Expense)									57	65	55
Net Income									856	760	644
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									844	595	909
Net Cash Provided By (Used In) Operating Activities									571	577	288
Net Cash Provided By (Used In) Investing Activities									(366)	148	(395)
Net Cash Provided By (Used In) Financing Activities									(205)	(724)	$ 107
Current Assets	4,501				4,263				4,501	4,263
Property, Plant and Equipment, net	83				81				83	81
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	4,501				4,516				4,501	4,516
Noncurrent Assets	155				269				155	269
Total Assets	9,240				9,129				9,240	9,129
Current Liabilities	1,112				883				1,112	883
Noncurrent Liabilities	442				454				442	454
Total Long-Term Debt	1,684				2,234				1,684	2,234
Member's Equity	6,002				5,558				6,002	5,558
TOTAL LIABILITIES AND CAPITALIZATION	$ 9,240				$ 9,129				$ 9,240	$ 9,129