Guarantees Of Debt (Schedule Of Financial Statements Of Guarantors) (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Guarantees of Debt [Line Items]
Operating Revenues	$ 2,096	$ 2,263	$ 2,133	$ 2,592	$ 2,090	$ 2,450	$ 1,905	$ 2,616	$ 9,084	$ 9,061	$ 10,415
Operating Expenses									7,655	7,485	7,453
Operating Income (Loss)	362	693	196	178	(175)	577	347	827	1,429	1,576	2,962
Equity Earnings (Losses) of Subsidiaries									14	11	12
Other Income									319	191	254
Other Deductions									(91)	(67)	(102)
Other-than-Temporary-Impairments									(12)	(28)	(53)
Interest Expense									(391)	(385)	(393)
Income Tax Benefit (Expense)									306	(411)	(1,001)
Net Income									1,574	887	1,679
Net Cash Provided By (Used In) Operating Activities									3,261	3,311	3,919
Net Cash Provided By (Used In) Investing Activities									(4,256)	(4,248)	(3,942)
Net Cash Provided By (Used In) Financing Activities									885	966	15
Current Assets	3,312				3,254				3,312	3,254
Property, Plant and Equipment, net	31,797				29,286				31,797	29,286
Noncurrent Assets	7,607				7,530				7,607	7,530
Total Assets	42,716				40,070				42,716	40,070	37,535
Current Liabilities	4,168				3,276				4,168	3,276
Noncurrent Liabilities	12,633				12,769				12,633	12,769
Total Long-Term Debt	12,068				10,895				12,068	10,895
Member's Equity	13,847				13,130				13,847	13,130	13,067	$ 12,186
TOTAL LIABILITIES AND CAPITALIZATION	42,716				40,070				42,716	40,070
Power [Member]
Guarantees of Debt [Line Items]
Operating Revenues	844	873	929	1,284	921	1,075	714	1,313	3,930	4,023	4,928
Operating Expenses									4,289	4,010	3,498
Operating Income (Loss)	(82)	$ 213	$ (187)	$ (303)	(556)	$ 238	$ (12)	$ 343	(359)	13	1,430
Equity Earnings (Losses) of Subsidiaries									14	11	14
Other Income									213	102	169
Other Deductions									(56)	(57)	(72)
Other-than-Temporary-Impairments									(12)	(28)	(53)
Interest Expense									(50)	(84)	(121)
Income Tax Benefit (Expense)									729	61	(511)
Net Income									479	18	856
Net Cash Provided By (Used In) Operating Activities									1,326	1,255	1,706
Net Cash Provided By (Used In) Investing Activities									(1,232)	(1,147)	(1,001)
Net Cash Provided By (Used In) Financing Activities									(73)	(109)	(702)
Current Assets	1,341				1,460				1,341	1,460
Property, Plant and Equipment, net	8,596				8,520				8,596	8,520
Noncurrent Assets	2,481				2,213				2,481	2,213
Total Assets	12,418				12,193				12,418	12,193
Current Liabilities	1,435				680				1,435	680
Noncurrent Liabilities	2,880				3,332				2,880	3,332
Total Long-Term Debt	2,136				2,382				2,136	2,382
Member's Equity	5,967				5,799				5,967	5,799	6,002	$ 5,558
TOTAL LIABILITIES AND CAPITALIZATION	12,418				12,193				12,418	12,193
Power Senior Notes [Member]
Guarantees of Debt [Line Items]
Operating Revenues									3,930	4,023	4,928
Operating Expenses									4,289	4,010	3,498
Operating Income (Loss)									(359)	13	1,430
Equity Earnings (Losses) of Subsidiaries									14	11	14
Other Income									213	102	169
Other Deductions									(56)	(57)	(72)
Other-than-Temporary-Impairments									(12)	(28)	(53)
Interest Expense									(50)	(84)	(121)
Income Tax Benefit (Expense)									729	61	(511)
Net Income									479	18	856
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									518	47	844
Net Cash Provided By (Used In) Operating Activities									1,326	1,255	1,706
Net Cash Provided By (Used In) Investing Activities									(1,232)	(1,147)	(1,001)
Net Cash Provided By (Used In) Financing Activities									(73)	(109)	(702)
Current Assets	1,341				1,460				1,341	1,460
Property, Plant and Equipment, net	8,596				8,520				8,596	8,520
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0				0				0	0
Noncurrent Assets	2,481				2,213				2,481	2,213
Total Assets	12,418				12,193				12,418	12,193
Current Liabilities	1,435				680				1,435	680
Noncurrent Liabilities	2,880				3,332				2,880	3,332
Total Long-Term Debt	2,136				2,382				2,136	2,382
Member's Equity	5,967				5,799				5,967	5,799
TOTAL LIABILITIES AND CAPITALIZATION	12,418				12,193				12,418	12,193
Power Senior Notes [Member] | Guarantor Subsidiaries [Member]
Guarantees of Debt [Line Items]
Operating Revenues									3,891	3,971	4,883
Operating Expenses									4,221	3,962	3,451
Operating Income (Loss)									(330)	9	1,432
Equity Earnings (Losses) of Subsidiaries									60	(3)	(4)
Other Income									257	120	174
Other Deductions									(32)	(39)	(45)
Other-than-Temporary-Impairments									(12)	(28)	(53)
Interest Expense									(49)	(40)	(39)
Income Tax Benefit (Expense)									588	(11)	(574)
Net Income									482	8	891
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									529	50	855
Net Cash Provided By (Used In) Operating Activities									1,185	1,442	2,089
Net Cash Provided By (Used In) Investing Activities									(448)	(707)	(1,519)
Net Cash Provided By (Used In) Financing Activities									(736)	(736)	(571)
Current Assets	1,500				1,593				1,500	1,593
Property, Plant and Equipment, net	5,778				6,145				5,778	6,145
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	404				344				404	344
Noncurrent Assets	2,349				2,016				2,349	2,016
Total Assets	10,031				10,098				10,031	10,098
Current Liabilities	3,586				3,752				3,586	3,752
Noncurrent Liabilities	1,966				2,398				1,966	2,398
Total Long-Term Debt	0				0				0	0
Member's Equity	4,479				3,948				4,479	3,948
TOTAL LIABILITIES AND CAPITALIZATION	10,031				10,098				10,031	10,098
Power Senior Notes [Member] | Non-Guarantor Subsidiaries [Member]
Guarantees of Debt [Line Items]
Operating Revenues									174	173	179
Operating Expenses									195	161	169
Operating Income (Loss)									(21)	12	10
Equity Earnings (Losses) of Subsidiaries									14	11	14
Other Income									2	0	0
Other Deductions									0	0	0
Other-than-Temporary-Impairments									0	0	0
Interest Expense									(17)	(18)	(19)
Income Tax Benefit (Expense)									167	20	6
Net Income									145	25	11
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									145	25	11
Net Cash Provided By (Used In) Operating Activities									238	323	80
Net Cash Provided By (Used In) Investing Activities									(525)	(789)	(430)
Net Cash Provided By (Used In) Financing Activities									307	466	354
Current Assets	200				152				200	152
Property, Plant and Equipment, net	2,764				2,320				2,764	2,320
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0				0				0	0
Noncurrent Assets	110				129				110	129
Total Assets	3,074				2,601				3,074	2,601
Current Liabilities	1,846				1,454				1,846	1,454
Noncurrent Liabilities	459				502				459	502
Total Long-Term Debt	0				0				0	0
Member's Equity	769				645				769	645
TOTAL LIABILITIES AND CAPITALIZATION	3,074				2,601				3,074	2,601
Power Senior Notes [Member] | Power Parent [Member]
Guarantees of Debt [Line Items]
Operating Revenues									0	0	0
Operating Expenses									8	8	12
Operating Income (Loss)									(8)	(8)	(12)
Equity Earnings (Losses) of Subsidiaries									567	36	906
Other Income									98	71	48
Other Deductions									(24)	(18)	(27)
Other-than-Temporary-Impairments									0	0	0
Interest Expense									(128)	(115)	(116)
Income Tax Benefit (Expense)									(26)	52	57
Net Income									479	18	856
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									518	47	844
Net Cash Provided By (Used In) Operating Activities									(42)	97	571
Net Cash Provided By (Used In) Investing Activities									506	60	(366)
Net Cash Provided By (Used In) Financing Activities									(464)	(157)	(205)
Current Assets	4,327				4,412				4,327	4,412
Property, Plant and Equipment, net	54				55				54	55
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	4,844				4,249				4,844	4,249
Noncurrent Assets	100				168				100	168
Total Assets	9,325				8,884				9,325	8,884
Current Liabilities	689				171				689	171
Noncurrent Liabilities	533				532				533	532
Total Long-Term Debt	2,136				2,382				2,136	2,382
Member's Equity	5,967				5,799				5,967	5,799
TOTAL LIABILITIES AND CAPITALIZATION	9,325				8,884				9,325	8,884
Consolidation, Eliminations [Member] | Power Senior Notes [Member]
Guarantees of Debt [Line Items]
Operating Revenues									(135)	(121)	(134)
Operating Expenses									(135)	(121)	(134)
Operating Income (Loss)									0	0	0
Equity Earnings (Losses) of Subsidiaries									(627)	(33)	(902)
Other Income									(144)	(89)	(53)
Other Deductions									0	0	0
Other-than-Temporary-Impairments									0	0	0
Interest Expense									144	89	53
Income Tax Benefit (Expense)									0	0	0
Net Income									(627)	(33)	(902)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									(674)	(75)	(866)
Net Cash Provided By (Used In) Operating Activities									(55)	(607)	(1,034)
Net Cash Provided By (Used In) Investing Activities									(765)	289	1,314
Net Cash Provided By (Used In) Financing Activities									820	318	$ (280)
Current Assets	(4,686)				(4,697)				(4,686)	(4,697)
Property, Plant and Equipment, net	0				0				0	0
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	(5,248)				(4,593)				(5,248)	(4,593)
Noncurrent Assets	(78)				(100)				(78)	(100)
Total Assets	(10,012)				(9,390)				(10,012)	(9,390)
Current Liabilities	(4,686)				(4,697)				(4,686)	(4,697)
Noncurrent Liabilities	(78)				(100)				(78)	(100)
Total Long-Term Debt	0				0				0	0
Member's Equity	(5,248)				(4,593)				(5,248)	(4,593)
TOTAL LIABILITIES AND CAPITALIZATION	$ (10,012)				$ (9,390)				$ (10,012)	$ (9,390)