Guarantees Of Debt (Schedule Of Financial Statements Of Guarantors) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Operating Revenues	$ 2,016	$ 2,142	$ 4,834	$ 4,733
Operating Expenses	1,605	1,947	3,591	4,360
Operating Income (Loss)	411	195	1,243	373
Equity Earnings (Losses) of Subsidiaries	5	5	7	8
Net Gains (Losses) on Trust Investments	8	25	(14)	53
Other Income (Deductions)	34	33	66	65
Non-Operating Pension and OPEB Credits (Costs)	19	1	38	1
Interest Expense	(111)	(91)	(214)	(189)
Income Tax Benefit (Expense)	(97)	(59)	(299)	(88)
Net Income (Loss)	269	109	827	223
Net Cash Provided By (Used In) Operating Activities			1,633	1,755
Net Cash Provided By (Used In) Investing Activities			(2,027)	(1,989)
Net Cash Provided By (Used In) Financing Activities			190	240
Current Assets	3,005		3,005		$ 3,312
Property, Plant and Equipment, net	33,151		33,151		31,797
Noncurrent Assets	7,551		7,551		7,607
Total Assets	43,707		43,707		42,716
Current Liabilities	4,244		4,244		4,168
Noncurrent Liabilities	12,795		12,795		12,633
Long-Term Debt	12,510		12,510		12,068
Member's Equity	14,158		14,158		13,847
TOTAL LIABILITIES AND CAPITALIZATION	43,707		43,707		42,716
Power [Member]
Debt Instrument [Line Items]
Operating Revenues	767	918	2,170	2,187
Operating Expenses	725	1,107	1,799	2,681
Operating Income (Loss)	42	(189)	371	(494)
Equity Earnings (Losses) of Subsidiaries	5	5	7	8
Net Gains (Losses) on Trust Investments	8	24	(14)	43
Other Income (Deductions)	13	12	24	23
Non-Operating Pension and OPEB Credits (Costs)	3	2	7	4
Interest Expense	(11)	(13)	(18)	(29)
Income Tax Benefit (Expense)	(19)	62	(102)	178
Net Income (Loss)	41	(97)	275	(267)
Net Cash Provided By (Used In) Operating Activities			869	932
Net Cash Provided By (Used In) Investing Activities			(1,095)	(735)
Net Cash Provided By (Used In) Financing Activities			214	(179)
Current Assets	1,565		1,565		1,341
Property, Plant and Equipment, net	8,779		8,779		8,596
Noncurrent Assets	2,428		2,428		2,481
Total Assets	12,772		12,772		12,418
Current Liabilities	973		973		1,435
Noncurrent Liabilities	2,927		2,927		2,880
Long-Term Debt	2,833		2,833		2,136
Member's Equity	6,039		6,039		5,967
TOTAL LIABILITIES AND CAPITALIZATION	12,772		12,772		12,418
Power Senior Notes [Member] | Consolidating Adjustments [Member]
Debt Instrument [Line Items]
Operating Revenues	(31)	(28)	(65)	(66)
Operating Expenses	(31)	(28)	(65)	(66)
Operating Income (Loss)	0	0	0	0
Equity Earnings (Losses) of Subsidiaries	(51)	97	(282)	259
Net Gains (Losses) on Trust Investments	0	0	0	0
Other Income (Deductions)	(68)	(34)	(125)	(62)
Non-Operating Pension and OPEB Credits (Costs)	0	0	0	0
Interest Expense	68	34	125	62
Income Tax Benefit (Expense)	0	0	0	0
Net Income (Loss)	(51)	97	(282)	259
Comprehensive Income (Loss)	(48)	88	(269)	229
Net Cash Provided By (Used In) Operating Activities			98	51
Net Cash Provided By (Used In) Investing Activities			808	(1,355)
Net Cash Provided By (Used In) Financing Activities			(906)	1,304
Current Assets	(4,868)		(4,868)		(4,686)
Property, Plant and Equipment, net	0		0		0
Investment in Subsidiaries	(6,106)		(6,106)		(5,248)
Noncurrent Assets	(183)		(183)		(78)
Total Assets	(11,157)		(11,157)		(10,012)
Current Liabilities	(4,868)		(4,868)		(4,686)
Noncurrent Liabilities	(183)		(183)		(78)
Long-Term Debt	0		0		0
Member's Equity	(6,106)		(6,106)		(5,248)
TOTAL LIABILITIES AND CAPITALIZATION	(11,157)		(11,157)		(10,012)
Power Senior Notes [Member] | Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	747	899	2,133	2,154
Operating Expenses	704	1,094	1,760	2,650
Operating Income (Loss)	43	(195)	373	(496)
Equity Earnings (Losses) of Subsidiaries	(4)	(4)	(7)	(5)
Net Gains (Losses) on Trust Investments	8	25	(14)	40
Other Income (Deductions)	40	21	73	40
Non-Operating Pension and OPEB Credits (Costs)	2	2	6	4
Interest Expense	(19)	(9)	(36)	(18)
Income Tax Benefit (Expense)	(23)	60	(115)	171
Net Income (Loss)	47	(100)	280	(264)
Comprehensive Income (Loss)	44	(91)	267	(234)
Net Cash Provided By (Used In) Operating Activities			745	802
Net Cash Provided By (Used In) Investing Activities			(867)	178
Net Cash Provided By (Used In) Financing Activities			123	(978)
Current Assets	1,411		1,411		1,500
Property, Plant and Equipment, net	5,048		5,048		5,778
Investment in Subsidiaries	1,129		1,129		404
Noncurrent Assets	2,258		2,258		2,349
Total Assets	9,846		9,846		10,031
Current Liabilities	3,164		3,164		3,586
Noncurrent Liabilities	2,097		2,097		1,966
Long-Term Debt	0		0		0
Member's Equity	4,585		4,585		4,479
TOTAL LIABILITIES AND CAPITALIZATION	9,846		9,846		10,031
Power Senior Notes [Member] | Non-Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	51	47	102	99
Operating Expenses	49	43	101	95
Operating Income (Loss)	2	4	1	4
Equity Earnings (Losses) of Subsidiaries	5	5	7	8
Net Gains (Losses) on Trust Investments	0	0	0	0
Other Income (Deductions)	0	2	0	2
Non-Operating Pension and OPEB Credits (Costs)	1	0	1	0
Interest Expense	(6)	(4)	(11)	(9)
Income Tax Benefit (Expense)	2	(4)	4	0
Net Income (Loss)	4	3	2	5
Comprehensive Income (Loss)	4	3	2	5
Net Cash Provided By (Used In) Operating Activities			(8)	111
Net Cash Provided By (Used In) Investing Activities			(196)	(241)
Net Cash Provided By (Used In) Financing Activities			191	146
Current Assets	216		216		200
Property, Plant and Equipment, net	3,679		3,679		2,764
Investment in Subsidiaries	0		0		0
Noncurrent Assets	110		110		110
Total Assets	4,005		4,005		3,074
Current Liabilities	1,987		1,987		1,846
Noncurrent Liabilities	497		497		459
Long-Term Debt	0		0		0
Member's Equity	1,521		1,521		769
TOTAL LIABILITIES AND CAPITALIZATION	4,005		4,005		3,074
Power Senior Notes [Member] | Power Parent [Member]
Debt Instrument [Line Items]
Operating Revenues	0	0	0	0
Operating Expenses	3	(2)	3	2
Operating Income (Loss)	(3)	2	(3)	(2)
Equity Earnings (Losses) of Subsidiaries	55	(93)	289	(254)
Net Gains (Losses) on Trust Investments	0	(1)	0	3
Other Income (Deductions)	41	23	76	43
Non-Operating Pension and OPEB Credits (Costs)	0	0	0	0
Interest Expense	(54)	(34)	(96)	(64)
Income Tax Benefit (Expense)	2	6	9	7
Net Income (Loss)	41	(97)	275	(267)
Comprehensive Income (Loss)	43	(82)	272	(228)
Net Cash Provided By (Used In) Operating Activities			34	(32)
Net Cash Provided By (Used In) Investing Activities			(840)	683
Net Cash Provided By (Used In) Financing Activities			806	(651)
Current Assets	4,806		4,806		4,327
Property, Plant and Equipment, net	52		52		54
Investment in Subsidiaries	4,977		4,977		4,844
Noncurrent Assets	243		243		100
Total Assets	10,078		10,078		9,325
Current Liabilities	690		690		689
Noncurrent Liabilities	516		516		533
Long-Term Debt	2,833		2,833		2,136
Member's Equity	6,039		6,039		5,967
TOTAL LIABILITIES AND CAPITALIZATION	10,078		10,078		9,325
Power Senior Notes [Member] | Power [Member]
Debt Instrument [Line Items]
Operating Revenues	767	918	2,170	2,187
Operating Expenses	725	1,107	1,799	2,681
Operating Income (Loss)	42	(189)	371	(494)
Equity Earnings (Losses) of Subsidiaries	5	5	7	8
Net Gains (Losses) on Trust Investments	8	24	(14)	43
Other Income (Deductions)	13	12	24	23
Non-Operating Pension and OPEB Credits (Costs)	3	2	7	4
Interest Expense	(11)	(13)	(18)	(29)
Income Tax Benefit (Expense)	(19)	62	(102)	178
Net Income (Loss)	41	(97)	275	(267)
Comprehensive Income (Loss)	43	$ (82)	272	(228)
Net Cash Provided By (Used In) Operating Activities			869	932
Net Cash Provided By (Used In) Investing Activities			(1,095)	(735)
Net Cash Provided By (Used In) Financing Activities			214	$ (179)
Current Assets	1,565		1,565		1,341
Property, Plant and Equipment, net	8,779		8,779		8,596
Investment in Subsidiaries	0		0		0
Noncurrent Assets	2,428		2,428		2,481
Total Assets	12,772		12,772		12,418
Current Liabilities	973		973		1,435
Noncurrent Liabilities	2,927		2,927		2,880
Long-Term Debt	2,833		2,833		2,136
Member's Equity	6,039		6,039		5,967
TOTAL LIABILITIES AND CAPITALIZATION	$ 12,772		$ 12,772		$ 12,418