Guarantees Of Debt (Schedule Of Financial Statements Of Guarantors) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Operating Revenues	$ 2,394	$ 2,254	$ 7,228	$ 6,987
Operating Expenses	1,840	1,561	5,431	5,921
Operating Income (Loss)	554	693	1,797	1,066
Equity Earnings (Losses) of Subsidiaries	5	3	12	11
Net Gains (Losses) on Trust Investments	45	18	31	71
Other Income (Deductions)	33	33	99	98
Non-Operating Pension and OPEB Credits (Costs)	19	0	57	1
Interest Expense	(127)	(100)	(341)	(289)
Income Tax Benefit (Expense)	(117)	(252)	(416)	(340)
Net Income (Loss)	412	395	1,239	618
Net Cash Provided By (Used In) Operating Activities			2,492	2,733
Net Cash Provided By (Used In) Investing Activities			(3,113)	(3,104)
Net Cash Provided By (Used In) Financing Activities			412	225
Current Assets	3,215		3,215		$ 3,312
Property, Plant and Equipment, net	33,781		33,781		31,797
Noncurrent Assets	8,077		8,077		7,607
Total Assets	45,073		45,073		42,716
Current Liabilities	4,485		4,485		4,168
Noncurrent Liabilities	13,320		13,320		12,633
Long-Term Debt	12,909		12,909		12,068
Member's Equity	14,359		14,359		13,847
TOTAL LIABILITIES AND CAPITALIZATION	45,073		45,073		42,716
Power [Member]
Debt Instrument [Line Items]
Operating Revenues	868	846	3,038	3,033
Operating Expenses	756	635	2,555	3,316
Operating Income (Loss)	112	211	483	(283)
Equity Earnings (Losses) of Subsidiaries	5	3	12	11
Net Gains (Losses) on Trust Investments	44	19	30	62
Other Income (Deductions)	14	11	38	34
Non-Operating Pension and OPEB Credits (Costs)	4	2	11	6
Interest Expense	(29)	(12)	(47)	(41)
Income Tax Benefit (Expense)	(25)	(98)	(127)	80
Net Income (Loss)	125	136	400	(131)
Net Cash Provided By (Used In) Operating Activities			1,005	1,249
Net Cash Provided By (Used In) Investing Activities			(1,010)	(884)
Net Cash Provided By (Used In) Financing Activities			14	(354)
Current Assets	1,376		1,376		1,341
Property, Plant and Equipment, net	8,869		8,869		8,596
Noncurrent Assets	2,436		2,436		2,481
Total Assets	12,681		12,681		12,418
Current Liabilities	869		869		1,435
Noncurrent Liabilities	3,011		3,011		2,880
Long-Term Debt	2,834		2,834		2,136
Member's Equity	5,967		5,967		5,967
TOTAL LIABILITIES AND CAPITALIZATION	12,681		12,681		12,418
Power Senior Notes [Member] | Consolidating Adjustments [Member]
Debt Instrument [Line Items]
Operating Revenues	(40)	(29)	(105)	(95)
Operating Expenses	(40)	(29)	(105)	(95)
Operating Income (Loss)	0	0	0	0
Equity Earnings (Losses) of Subsidiaries	(110)	(140)	(392)	119
Net Gains (Losses) on Trust Investments	0	0	0	0
Other Income (Deductions)	(71)	(37)	(196)	(99)
Non-Operating Pension and OPEB Credits (Costs)	0	0	0	0
Interest Expense	71	37	196	99
Income Tax Benefit (Expense)	0	0	0	0
Net Income (Loss)	(110)	(140)	(392)	119
Comprehensive Income (Loss)	(106)	(154)	(375)	75
Net Cash Provided By (Used In) Operating Activities			117	3
Net Cash Provided By (Used In) Investing Activities			829	(990)
Net Cash Provided By (Used In) Financing Activities			(946)	987
Current Assets	(4,776)		(4,776)		(4,686)
Property, Plant and Equipment, net	0		0		0
Investment in Subsidiaries	(6,210)		(6,210)		(5,248)
Noncurrent Assets	(217)		(217)		(78)
Total Assets	(11,203)		(11,203)		(10,012)
Current Liabilities	(4,776)		(4,776)		(4,686)
Noncurrent Liabilities	(217)		(217)		(78)
Long-Term Debt	0		0		0
Member's Equity	(6,210)		(6,210)		(5,248)
TOTAL LIABILITIES AND CAPITALIZATION	(11,203)		(11,203)		(10,012)
Power Senior Notes [Member] | Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	849	829	2,982	2,983
Operating Expenses	733	618	2,493	3,268
Operating Income (Loss)	116	211	489	(285)
Equity Earnings (Losses) of Subsidiaries	(7)	(3)	(14)	(8)
Net Gains (Losses) on Trust Investments	45	19	31	59
Other Income (Deductions)	45	26	118	66
Non-Operating Pension and OPEB Credits (Costs)	4	2	10	6
Interest Expense	(28)	(12)	(64)	(30)
Income Tax Benefit (Expense)	(64)	(103)	(179)	68
Net Income (Loss)	111	140	391	(124)
Comprehensive Income (Loss)	107	154	374	(80)
Net Cash Provided By (Used In) Operating Activities			1,169	1,159
Net Cash Provided By (Used In) Investing Activities			(1,132)	(289)
Net Cash Provided By (Used In) Financing Activities			(32)	(869)
Current Assets	1,353		1,353		1,500
Property, Plant and Equipment, net	5,074		5,074		5,778
Investment in Subsidiaries	1,124		1,124		404
Noncurrent Assets	2,302		2,302		2,349
Total Assets	9,853		9,853		10,031
Current Liabilities	3,030		3,030		3,586
Noncurrent Liabilities	2,129		2,129		1,966
Long-Term Debt	0		0		0
Member's Equity	4,694		4,694		4,479
TOTAL LIABILITIES AND CAPITALIZATION	9,853		9,853		10,031
Power Senior Notes [Member] | Non-Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	59	46	161	145
Operating Expenses	61	44	162	139
Operating Income (Loss)	(2)	2	(1)	6
Equity Earnings (Losses) of Subsidiaries	5	3	12	11
Net Gains (Losses) on Trust Investments	(1)	0	(1)	0
Other Income (Deductions)	0	(2)	0	0
Non-Operating Pension and OPEB Credits (Costs)	0	0	1	0
Interest Expense	(7)	(5)	(18)	(14)
Income Tax Benefit (Expense)	4	2	8	2
Net Income (Loss)	(1)	0	1	5
Comprehensive Income (Loss)	(1)	0	1	5
Net Cash Provided By (Used In) Operating Activities			(26)	142
Net Cash Provided By (Used In) Investing Activities			(290)	(343)
Net Cash Provided By (Used In) Financing Activities			320	211
Current Assets	302		302		200
Property, Plant and Equipment, net	3,740		3,740		2,764
Investment in Subsidiaries	0		0		0
Noncurrent Assets	106		106		110
Total Assets	4,148		4,148		3,074
Current Liabilities	1,999		1,999		1,846
Noncurrent Liabilities	633		633		459
Long-Term Debt	0		0		0
Member's Equity	1,516		1,516		769
TOTAL LIABILITIES AND CAPITALIZATION	4,148		4,148		3,074
Power Senior Notes [Member] | Power Parent [Member]
Debt Instrument [Line Items]
Operating Revenues	0	0	0	0
Operating Expenses	2	2	5	4
Operating Income (Loss)	(2)	(2)	(5)	(4)
Equity Earnings (Losses) of Subsidiaries	117	143	406	(111)
Net Gains (Losses) on Trust Investments	0	0	0	3
Other Income (Deductions)	40	24	116	67
Non-Operating Pension and OPEB Credits (Costs)	0	0	0	0
Interest Expense	(65)	(32)	(161)	(96)
Income Tax Benefit (Expense)	35	3	44	10
Net Income (Loss)	125	136	400	(131)
Comprehensive Income (Loss)	128	156	400	(72)
Net Cash Provided By (Used In) Operating Activities			(255)	(55)
Net Cash Provided By (Used In) Investing Activities			(417)	738
Net Cash Provided By (Used In) Financing Activities			672	(683)
Current Assets	4,497		4,497		4,327
Property, Plant and Equipment, net	55		55		54
Investment in Subsidiaries	5,086		5,086		4,844
Noncurrent Assets	245		245		100
Total Assets	9,883		9,883		9,325
Current Liabilities	616		616		689
Noncurrent Liabilities	466		466		533
Long-Term Debt	2,834		2,834		2,136
Member's Equity	5,967		5,967		5,967
TOTAL LIABILITIES AND CAPITALIZATION	9,883		9,883		9,325
Power Senior Notes [Member] | Power [Member]
Debt Instrument [Line Items]
Operating Revenues	868	846	3,038	3,033
Operating Expenses	756	635	2,555	3,316
Operating Income (Loss)	112	211	483	(283)
Equity Earnings (Losses) of Subsidiaries	5	3	12	11
Net Gains (Losses) on Trust Investments	44	19	30	62
Other Income (Deductions)	14	11	38	34
Non-Operating Pension and OPEB Credits (Costs)	4	2	11	6
Interest Expense	(29)	(12)	(47)	(41)
Income Tax Benefit (Expense)	(25)	(98)	(127)	80
Net Income (Loss)	125	136	400	(131)
Comprehensive Income (Loss)	128	$ 156	400	(72)
Net Cash Provided By (Used In) Operating Activities			1,005	1,249
Net Cash Provided By (Used In) Investing Activities			(1,010)	(884)
Net Cash Provided By (Used In) Financing Activities			14	$ (354)
Current Assets	1,376		1,376		1,341
Property, Plant and Equipment, net	8,869		8,869		8,596
Investment in Subsidiaries	0		0		0
Noncurrent Assets	2,436		2,436		2,481
Total Assets	12,681		12,681		12,418
Current Liabilities	869		869		1,435
Noncurrent Liabilities	3,011		3,011		2,880
Long-Term Debt	2,834		2,834		2,136
Member's Equity	5,967		5,967		5,967
TOTAL LIABILITIES AND CAPITALIZATION	$ 12,681		$ 12,681		$ 12,418