Guarantees Of Debt (Schedule Of Financial Statements Of Guarantors) (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Guarantees of Debt [Line Items]
Operating Revenues	$ 2,090	$ 2,450	$ 1,905	$ 2,616	$ 2,278	$ 2,688	$ 2,314	$ 3,135	$ 9,061	$ 10,415	$ 10,886
Operating Expenses									7,485	7,453	8,263
Operating Income (Loss)	(175)	577	347	827	532	814	568	1,048	1,576	2,962	2,623
Equity Earnings (Losses) of Subsidiaries									11	12	13
Other Income									191	254	290
Other Deductions									(67)	(102)	(61)
Other-than-Temporary-Impairments									(28)	(53)	(20)
Interest Expense									(385)	(393)	(389)
Income Tax Benefit (Expense)									(411)	(1,001)	(938)
Net Income									887	1,679	1,518
Net Cash Provided By (Used In) Operating Activities									3,311	3,919	3,160
Net Cash Provided By (Used In) Investing Activities									(4,248)	(3,942)	(2,892)
Net Cash Provided By (Used In) Financing Activities									966	15	(359)
Current Assets	3,254				3,494				3,254	3,494
Property, Plant and Equipment, net	29,286				26,539				29,286	26,539
Noncurrent Assets	7,530				7,502				7,530	7,502
Total Assets	40,070				37,535				40,070	37,535	35,287
Current Liabilities	3,276				3,575				3,276	3,575
Noncurrent Liabilities	12,769				12,059				12,769	12,059
Total Long-Term Debt	10,895				8,834				10,895	8,834
Member's Equity	13,130				13,067				13,130	13,067	12,186	$ 11,609
TOTAL LIABILITIES AND CAPITALIZATION	40,070				37,535				40,070	37,535
Power [Member]
Guarantees of Debt [Line Items]
Operating Revenues	921	1,075	714	1,313	1,082	1,096	1,025	1,725	4,023	4,928	5,434
Operating Expenses									4,010	3,498	4,225
Operating Income (Loss)	(556)	$ 238	$ (12)	$ 343	227	$ 391	$ 228	$ 584	13	1,430	1,209
Equity Earnings (Losses) of Subsidiaries									11	14	14
Other Income									102	169	222
Other Deductions									(57)	(72)	(52)
Other-than-Temporary-Impairments									(28)	(53)	(20)
Interest Expense									(84)	(121)	(122)
Income Tax Benefit (Expense)									61	(511)	(491)
Net Income									18	856	760
Net Cash Provided By (Used In) Operating Activities									1,255	1,706	1,425
Net Cash Provided By (Used In) Investing Activities									(1,147)	(1,001)	(524)
Net Cash Provided By (Used In) Financing Activities									(109)	(702)	(898)
Current Assets	1,460				1,949				1,460	1,949
Property, Plant and Equipment, net	8,520				8,127				8,520	8,127
Noncurrent Assets	2,213				2,174				2,213	2,174
Total Assets	12,193				12,250				12,193	12,250
Current Liabilities	680				1,226				680	1,226
Noncurrent Liabilities	3,332				3,338				3,332	3,338
Total Long-Term Debt	2,382				1,684				2,382	1,684
Member's Equity	5,799				6,002				5,799	6,002	5,558	$ 5,858
TOTAL LIABILITIES AND CAPITALIZATION	12,193				12,250				12,193	12,250
Power Senior Notes [Member]
Guarantees of Debt [Line Items]
Operating Revenues									4,023	4,928	5,434
Operating Expenses									4,010	3,498	4,225
Operating Income (Loss)									13	1,430	1,209
Equity Earnings (Losses) of Subsidiaries									11	14	14
Other Income									102	169	222
Other Deductions									(57)	(72)	(52)
Other-than-Temporary-Impairments									(28)	(53)	(20)
Interest Expense									(84)	(121)	(122)
Income Tax Benefit (Expense)									61	(511)	(491)
Net Income									18	856	760
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									47	844	595
Net Cash Provided By (Used In) Operating Activities									1,255	1,706	1,425
Net Cash Provided By (Used In) Investing Activities									(1,147)	(1,001)	(524)
Net Cash Provided By (Used In) Financing Activities									(109)	(702)	(898)
Current Assets	1,460				1,949				1,460	1,949
Property, Plant and Equipment, net	8,520				8,127				8,520	8,127
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0				0				0	0
Noncurrent Assets	2,213				2,174				2,213	2,174
Total Assets	12,193				12,250				12,193	12,250
Current Liabilities	680				1,226				680	1,226
Noncurrent Liabilities	3,332				3,338				3,332	3,338
Total Long-Term Debt	2,382				1,684				2,382	1,684
Member's Equity	5,799				6,002				5,799	6,002
TOTAL LIABILITIES AND CAPITALIZATION	12,193				12,250				12,193	12,250
Power Senior Notes [Member] | Guarantor Subsidiaries [Member]
Guarantees of Debt [Line Items]
Operating Revenues									3,971	4,883	5,390
Operating Expenses									3,962	3,451	4,175
Operating Income (Loss)									9	1,432	1,215
Equity Earnings (Losses) of Subsidiaries									(3)	(4)	(5)
Other Income									120	174	222
Other Deductions									(39)	(45)	(32)
Other-than-Temporary-Impairments									(28)	(53)	(20)
Interest Expense									(40)	(39)	(35)
Income Tax Benefit (Expense)									(11)	(574)	(558)
Net Income									8	891	787
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									50	855	768
Net Cash Provided By (Used In) Operating Activities									1,442	2,089	1,674
Net Cash Provided By (Used In) Investing Activities									(707)	(1,519)	(856)
Net Cash Provided By (Used In) Financing Activities									(736)	(571)	(818)
Current Assets	1,593				1,912				1,593	1,912
Property, Plant and Equipment, net	6,145				6,502				6,145	6,502
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	344				346				344	346
Noncurrent Assets	2,016				1,959				2,016	1,959
Total Assets	10,098				10,719				10,098	10,719
Current Liabilities	3,752				3,866				3,752	3,866
Noncurrent Liabilities	2,398				2,597				2,398	2,597
Total Long-Term Debt	0				0				0	0
Member's Equity	3,948				4,256				3,948	4,256
TOTAL LIABILITIES AND CAPITALIZATION	10,098				10,719				10,098	10,719
Power Senior Notes [Member] | Non-Guarantor Subsidiaries [Member]
Guarantees of Debt [Line Items]
Operating Revenues									173	179	153
Operating Expenses									161	169	143
Operating Income (Loss)									12	10	10
Equity Earnings (Losses) of Subsidiaries									11	14	14
Other Income									0	0	0
Other Deductions									0	0	0
Other-than-Temporary-Impairments									0	0	0
Interest Expense									(18)	(19)	(19)
Income Tax Benefit (Expense)									20	6	2
Net Income									25	11	7
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									25	11	7
Net Cash Provided By (Used In) Operating Activities									323	80	76
Net Cash Provided By (Used In) Investing Activities									(789)	(430)	(42)
Net Cash Provided By (Used In) Financing Activities									466	354	(32)
Current Assets	152				364				152	364
Property, Plant and Equipment, net	2,320				1,542				2,320	1,542
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0				0				0	0
Noncurrent Assets	129				136				129	136
Total Assets	2,601				2,042				2,601	2,042
Current Liabilities	1,454				1,076				1,454	1,076
Noncurrent Liabilities	502				375				502	375
Total Long-Term Debt	0				0				0	0
Member's Equity	645				591				645	591
TOTAL LIABILITIES AND CAPITALIZATION	2,601				2,042				2,601	2,042
Power Senior Notes [Member] | Power Parent [Member]
Guarantees of Debt [Line Items]
Operating Revenues									0	0	0
Operating Expenses									8	12	16
Operating Income (Loss)									(8)	(12)	(16)
Equity Earnings (Losses) of Subsidiaries									36	906	799
Other Income									71	48	34
Other Deductions									(18)	(27)	(20)
Other-than-Temporary-Impairments									0	0	0
Interest Expense									(115)	(116)	(102)
Income Tax Benefit (Expense)									52	57	65
Net Income									18	856	760
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									47	844	595
Net Cash Provided By (Used In) Operating Activities									97	571	577
Net Cash Provided By (Used In) Investing Activities									60	(366)	148
Net Cash Provided By (Used In) Financing Activities									(157)	(205)	(724)
Current Assets	4,412				4,501				4,412	4,501
Property, Plant and Equipment, net	55				83				55	83
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	4,249				4,501				4,249	4,501
Noncurrent Assets	168				155				168	155
Total Assets	8,884				9,240				8,884	9,240
Current Liabilities	171				1,112				171	1,112
Noncurrent Liabilities	532				442				532	442
Total Long-Term Debt	2,382				1,684				2,382	1,684
Member's Equity	5,799				6,002				5,799	6,002
TOTAL LIABILITIES AND CAPITALIZATION	8,884				9,240				8,884	9,240
Consolidation, Eliminations [Member] | Power Senior Notes [Member]
Guarantees of Debt [Line Items]
Operating Revenues									(121)	(134)	(109)
Operating Expenses									(121)	(134)	(109)
Operating Income (Loss)									0	0	0
Equity Earnings (Losses) of Subsidiaries									(33)	(902)	(794)
Other Income									(89)	(53)	(34)
Other Deductions									0	0	0
Other-than-Temporary-Impairments									0	0	0
Interest Expense									89	53	34
Income Tax Benefit (Expense)									0	0	0
Net Income									(33)	(902)	(794)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									(75)	(866)	(775)
Net Cash Provided By (Used In) Operating Activities									(607)	(1,034)	(902)
Net Cash Provided By (Used In) Investing Activities									289	1,314	226
Net Cash Provided By (Used In) Financing Activities									318	(280)	$ 676
Current Assets	(4,697)				(4,828)				(4,697)	(4,828)
Property, Plant and Equipment, net	0				0				0	0
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	(4,593)				(4,847)				(4,593)	(4,847)
Noncurrent Assets	(100)				(76)				(100)	(76)
Total Assets	(9,390)				(9,751)				(9,390)	(9,751)
Current Liabilities	(4,697)				(4,828)				(4,697)	(4,828)
Noncurrent Liabilities	(100)				(76)				(100)	(76)
Total Long-Term Debt	0				0				0	0
Member's Equity	(4,593)				(4,847)				(4,593)	(4,847)
TOTAL LIABILITIES AND CAPITALIZATION	$ (9,390)				$ (9,751)				$ (9,390)	$ (9,751)