Guarantees Of Debt (Schedule Of Financial Statements Of Guarantors) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Operating Revenues	$ 2,980	$ 2,818
Operating Expenses	2,194	1,986
Operating Income (Loss)	786	832
Equity Earnings (Losses) of Subsidiaries	2	2
Net Gains (Losses) on Trust Investments	128	(22)
Other Income (Deductions)	33	32
Non-Operating Pension and OPEB Credits (Costs)	33	19
Interest Expense	(133)	(103)
Income Tax Benefit (Expense)	(149)	(202)
Net Income	700	558
Net Cash Provided By (Used In) Operating Activities	1,218	1,140
Net Cash Provided By (Used In) Investing Activities	(816)	(1,073)
Net Cash Provided By (Used In) Financing Activities	(505)	(248)
Current Assets	3,027		$ 3,507
Property, Plant and Equipment, net	34,787		34,363
Noncurrent Assets	7,942		7,456
Total Assets	45,756		45,326
Current Liabilities	4,473		4,935
Noncurrent Liabilities	13,253		12,846
Long-Term Debt	13,216		13,168
Member's Equity	14,814	14,104	14,377	$ 13,847
TOTAL LIABILITIES AND CAPITALIZATION	45,756		45,326
Power [Member]
Debt Instrument [Line Items]
Operating Revenues	1,416	1,403
Operating Expenses	1,115	1,074
Operating Income (Loss)	301	329
Equity Earnings (Losses) of Subsidiaries	2	2
Net Gains (Losses) on Trust Investments	126	(22)
Other Income (Deductions)	13	11
Non-Operating Pension and OPEB Credits (Costs)	3	4
Interest Expense	(25)	(7)
Income Tax Benefit (Expense)	(124)	(83)
Net Income	296	234
Net Cash Provided By (Used In) Operating Activities	726	542
Net Cash Provided By (Used In) Investing Activities	(276)	(317)
Net Cash Provided By (Used In) Financing Activities	(444)	(246)
Current Assets	1,312		1,507
Property, Plant and Equipment, net	8,876		8,842
Noncurrent Assets	2,483		2,245
Total Assets	12,671		12,594
Current Liabilities	638		842
Noncurrent Liabilities	3,175		3,001
Long-Term Debt	2,836		2,791
Member's Equity	6,022	6,196	5,960	$ 5,967
TOTAL LIABILITIES AND CAPITALIZATION	12,671		12,594
Power Senior Notes [Member] | Consolidating Adjustments [Member]
Debt Instrument [Line Items]
Operating Revenues	(41)	(34)
Operating Expenses	(41)	(34)
Operating Income (Loss)	0	0
Equity Earnings (Losses) of Subsidiaries	(301)	(231)
Net Gains (Losses) on Trust Investments	0	0
Other Income (Deductions)	(89)	(57)
Non-Operating Pension and OPEB Credits (Costs)	0	0
Interest Expense	89	57
Income Tax Benefit (Expense)	0	0
Net Income	(301)	(231)
Comprehensive Income (Loss)	(316)	(221)
Net Cash Provided By (Used In) Operating Activities	(94)	71
Net Cash Provided By (Used In) Investing Activities	728	605
Net Cash Provided By (Used In) Financing Activities	(634)	(677)
Current Assets	(5,217)		(4,593)
Property, Plant and Equipment, net	0		0
Investment in Subsidiaries	(6,408)		(6,169)
Noncurrent Assets	(209)		(238)
Total Assets	(11,834)		(11,000)
Current Liabilities	(5,217)		(4,593)
Noncurrent Liabilities	(209)		(238)
Long-Term Debt	0		0
Member's Equity	(6,408)		(6,169)
TOTAL LIABILITIES AND CAPITALIZATION	(11,834)		(11,000)
Power Senior Notes [Member] | Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	1,401	1,386
Operating Expenses	1,094	1,056
Operating Income (Loss)	307	330
Equity Earnings (Losses) of Subsidiaries	(8)	(3)
Net Gains (Losses) on Trust Investments	125	(22)
Other Income (Deductions)	55	33
Non-Operating Pension and OPEB Credits (Costs)	3	4
Interest Expense	(31)	(17)
Income Tax Benefit (Expense)	(144)	(92)
Net Income	307	233
Comprehensive Income (Loss)	322	223
Net Cash Provided By (Used In) Operating Activities	799	525
Net Cash Provided By (Used In) Investing Activities	(713)	(625)
Net Cash Provided By (Used In) Financing Activities	(86)	100
Current Assets	1,693		1,479
Property, Plant and Equipment, net	4,915		4,971
Investment in Subsidiaries	1,099		1,107
Noncurrent Assets	2,277		2,109
Total Assets	9,984		9,666
Current Liabilities	2,966		2,971
Noncurrent Liabilities	2,072		1,996
Long-Term Debt	0		0
Member's Equity	4,946		4,699
TOTAL LIABILITIES AND CAPITALIZATION	9,984		9,666
Power Senior Notes [Member] | Non-Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	56	51
Operating Expenses	61	52
Operating Income (Loss)	(5)	(1)
Equity Earnings (Losses) of Subsidiaries	2	2
Net Gains (Losses) on Trust Investments	0	0
Other Income (Deductions)	0	0
Non-Operating Pension and OPEB Credits (Costs)	0	0
Interest Expense	(8)	(5)
Income Tax Benefit (Expense)	5	2
Net Income	(6)	(2)
Comprehensive Income (Loss)	(6)	(2)
Net Cash Provided By (Used In) Operating Activities	43	(49)
Net Cash Provided By (Used In) Investing Activities	(124)	(82)
Net Cash Provided By (Used In) Financing Activities	87	111
Current Assets	318		304
Property, Plant and Equipment, net	3,913		3,822
Investment in Subsidiaries	0		0
Noncurrent Assets	137		101
Total Assets	4,368		4,227
Current Liabilities	2,113		2,027
Noncurrent Liabilities	793		730
Long-Term Debt	0		0
Member's Equity	1,462		1,470
TOTAL LIABILITIES AND CAPITALIZATION	4,368		4,227
Power Senior Notes [Member] | Power Parent [Member]
Debt Instrument [Line Items]
Operating Revenues	0	0
Operating Expenses	1	0
Operating Income (Loss)	(1)	0
Equity Earnings (Losses) of Subsidiaries	309	234
Net Gains (Losses) on Trust Investments	1	0
Other Income (Deductions)	47	35
Non-Operating Pension and OPEB Credits (Costs)	0	0
Interest Expense	(75)	(42)
Income Tax Benefit (Expense)	15	7
Net Income	296	234
Comprehensive Income (Loss)	312	229
Net Cash Provided By (Used In) Operating Activities	(22)	(5)
Net Cash Provided By (Used In) Investing Activities	(167)	(215)
Net Cash Provided By (Used In) Financing Activities	189	220
Current Assets	4,518		4,317
Property, Plant and Equipment, net	48		49
Investment in Subsidiaries	5,309		5,062
Noncurrent Assets	278		273
Total Assets	10,153		9,701
Current Liabilities	776		437
Noncurrent Liabilities	519		513
Long-Term Debt	2,836		2,791
Member's Equity	6,022		5,960
TOTAL LIABILITIES AND CAPITALIZATION	10,153		9,701
Power Senior Notes [Member] | Power [Member]
Debt Instrument [Line Items]
Operating Revenues	1,416	1,403
Operating Expenses	1,115	1,074
Operating Income (Loss)	301	329
Equity Earnings (Losses) of Subsidiaries	2	2
Net Gains (Losses) on Trust Investments	126	(22)
Other Income (Deductions)	13	11
Non-Operating Pension and OPEB Credits (Costs)	3	4
Interest Expense	(25)	(7)
Income Tax Benefit (Expense)	(124)	(83)
Net Income	296	234
Comprehensive Income (Loss)	312	229
Net Cash Provided By (Used In) Operating Activities	726	542
Net Cash Provided By (Used In) Investing Activities	(276)	(317)
Net Cash Provided By (Used In) Financing Activities	(444)	$ (246)
Current Assets	1,312		1,507
Property, Plant and Equipment, net	8,876		8,842
Investment in Subsidiaries	0		0
Noncurrent Assets	2,483		2,245
Total Assets	12,671		12,594
Current Liabilities	638		842
Noncurrent Liabilities	3,175		3,001
Long-Term Debt	2,836		2,791
Member's Equity	6,022		5,960
TOTAL LIABILITIES AND CAPITALIZATION	$ 12,671		$ 12,594