Guarantees Of Debt (Schedule Of Financial Statements Of Guarantors) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Operating Revenues	$ 2,818	$ 2,591
Operating Expenses	1,986	2,413
Operating Income (Loss)	832	178
Equity Earnings (Losses) of Subsidiaries	2	3
Net Gains (Losses) on Trust Investments	(22)	28
Other Income (Deductions)	32	32
Non-Operating Pension and Other Postretirement Plan Costs	(19)	0
Interest Expense	(103)	(98)
Income Tax Benefit (Expense)	(202)	(29)
Net Income (Loss)	558	114
Net Cash Provided By (Used In) Operating Activities	1,140	1,197
Net Cash Provided By (Used In) Investing Activities	(1,073)	(1,079)
Net Cash Provided By (Used In) Financing Activities	(248)	(347)
Current Assets	2,806		$ 3,312
Property, Plant and Equipment, net	32,405		31,797
Noncurrent Assets	7,579		7,607
Total Assets	42,790		42,716
Current Liabilities	3,948		4,168
Noncurrent Liabilities	12,666		12,633
Long-Term Debt	12,072		12,068
Member's Equity	14,104		13,847
TOTAL LIABILITIES AND CAPITALIZATION	42,790		42,716
Power [Member]
Debt Instrument [Line Items]
Operating Revenues	1,403	1,269
Operating Expenses	1,074	1,574
Operating Income (Loss)	329	(305)
Equity Earnings (Losses) of Subsidiaries	2	3
Net Gains (Losses) on Trust Investments	(22)	19
Other Income (Deductions)	11	11
Non-Operating Pension and Other Postretirement Plan Costs	(4)	(2)
Interest Expense	(7)	(16)
Income Tax Benefit (Expense)	(83)	116
Net Income (Loss)	234	(170)
Net Cash Provided By (Used In) Operating Activities	542	580
Net Cash Provided By (Used In) Investing Activities	(317)	(394)
Net Cash Provided By (Used In) Financing Activities	(246)	(179)
Current Assets	1,118		1,341
Property, Plant and Equipment, net	8,689		8,596
Noncurrent Assets	2,456		2,481
Total Assets	12,263		12,418
Current Liabilities	1,025		1,435
Noncurrent Liabilities	2,905		2,880
Long-Term Debt	2,137		2,136
Member's Equity	6,196		5,967
TOTAL LIABILITIES AND CAPITALIZATION	12,263		12,418
Power Senior Notes [Member] | Consolidating Adjustments [Member]
Debt Instrument [Line Items]
Operating Revenues	(34)	(38)
Operating Expenses	(34)	(38)
Operating Income (Loss)	0	0
Equity Earnings (Losses) of Subsidiaries	(231)	162
Net Gains (Losses) on Trust Investments	0	0
Other Income (Deductions)	(57)	(28)
Non-Operating Pension and Other Postretirement Plan Costs	0	0
Interest Expense	57	28
Income Tax Benefit (Expense)	0	0
Net Income (Loss)	(231)	162
Comprehensive Income (Loss)	(221)	141
Net Cash Provided By (Used In) Operating Activities	71	35
Net Cash Provided By (Used In) Investing Activities	605	(511)
Net Cash Provided By (Used In) Financing Activities	(677)	476
Current Assets	(4,631)		(4,686)
Property, Plant and Equipment, net	0		0
Investment in Subsidiaries	(6,204)		(5,248)
Noncurrent Assets	(38)		(78)
Total Assets	(10,873)		(10,012)
Current Liabilities	(4,631)		(4,686)
Noncurrent Liabilities	(38)		(78)
Long-Term Debt	0		0
Member's Equity	(6,204)		(5,248)
TOTAL LIABILITIES AND CAPITALIZATION	(10,873)		(10,012)
Power Senior Notes [Member] | Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	1,386	1,255
Operating Expenses	1,056	1,556
Operating Income (Loss)	330	(301)
Equity Earnings (Losses) of Subsidiaries	(3)	(1)
Net Gains (Losses) on Trust Investments	(22)	15
Other Income (Deductions)	33	19
Non-Operating Pension and Other Postretirement Plan Costs	(4)	(2)
Interest Expense	(17)	(9)
Income Tax Benefit (Expense)	(92)	111
Net Income (Loss)	233	(164)
Comprehensive Income (Loss)	223	(143)
Net Cash Provided By (Used In) Operating Activities	525	377
Net Cash Provided By (Used In) Investing Activities	(625)	20
Net Cash Provided By (Used In) Financing Activities	100	(395)
Current Assets	1,392		1,500
Property, Plant and Equipment, net	5,094		5,778
Investment in Subsidiaries	1,115		404
Noncurrent Assets	2,295		2,349
Total Assets	9,896		10,031
Current Liabilities	3,234		3,586
Noncurrent Liabilities	1,961		1,966
Long-Term Debt	0		0
Member's Equity	4,701		4,479
TOTAL LIABILITIES AND CAPITALIZATION	9,896		10,031
Power Senior Notes [Member] | Non-Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	51	52
Operating Expenses	52	52
Operating Income (Loss)	(1)	0
Equity Earnings (Losses) of Subsidiaries	2	3
Net Gains (Losses) on Trust Investments	0	0
Other Income (Deductions)	0	0
Non-Operating Pension and Other Postretirement Plan Costs	0	0
Interest Expense	(5)	(5)
Income Tax Benefit (Expense)	2	4
Net Income (Loss)	(2)	2
Comprehensive Income (Loss)	(2)	2
Net Cash Provided By (Used In) Operating Activities	(49)	91
Net Cash Provided By (Used In) Investing Activities	(82)	(154)
Net Cash Provided By (Used In) Financing Activities	111	68
Current Assets	189		200
Property, Plant and Equipment, net	3,540		2,764
Investment in Subsidiaries	0		0
Noncurrent Assets	109		110
Total Assets	3,838		3,074
Current Liabilities	1,874		1,846
Noncurrent Liabilities	461		459
Long-Term Debt	0		0
Member's Equity	1,503		769
TOTAL LIABILITIES AND CAPITALIZATION	3,838		3,074
Power Senior Notes [Member] | Power Parent [Member]
Debt Instrument [Line Items]
Operating Revenues	0	0
Operating Expenses	0	4
Operating Income (Loss)	0	(4)
Equity Earnings (Losses) of Subsidiaries	234	(161)
Net Gains (Losses) on Trust Investments	0	4
Other Income (Deductions)	35	20
Non-Operating Pension and Other Postretirement Plan Costs	0	0
Interest Expense	(42)	(30)
Income Tax Benefit (Expense)	7	1
Net Income (Loss)	234	(170)
Comprehensive Income (Loss)	229	(146)
Net Cash Provided By (Used In) Operating Activities	(5)	77
Net Cash Provided By (Used In) Investing Activities	(215)	251
Net Cash Provided By (Used In) Financing Activities	220	(328)
Current Assets	4,168		4,327
Property, Plant and Equipment, net	55		54
Investment in Subsidiaries	5,089		4,844
Noncurrent Assets	90		100
Total Assets	9,402		9,325
Current Liabilities	548		689
Noncurrent Liabilities	521		533
Long-Term Debt	2,137		2,136
Member's Equity	6,196		5,967
TOTAL LIABILITIES AND CAPITALIZATION	9,402		9,325
Power Senior Notes [Member] | Power [Member]
Debt Instrument [Line Items]
Operating Revenues	1,403	1,269
Operating Expenses	1,074	1,574
Operating Income (Loss)	329	(305)
Equity Earnings (Losses) of Subsidiaries	2	3
Net Gains (Losses) on Trust Investments	(22)	19
Other Income (Deductions)	11	11
Non-Operating Pension and Other Postretirement Plan Costs	(4)	(2)
Interest Expense	(7)	(16)
Income Tax Benefit (Expense)	(83)	116
Net Income (Loss)	234	(170)
Comprehensive Income (Loss)	229	(146)
Net Cash Provided By (Used In) Operating Activities	542	580
Net Cash Provided By (Used In) Investing Activities	(317)	(394)
Net Cash Provided By (Used In) Financing Activities	(246)	$ (179)
Current Assets	1,118		1,341
Property, Plant and Equipment, net	8,689		8,596
Investment in Subsidiaries	0		0
Noncurrent Assets	2,456		2,481
Total Assets	12,263		12,418
Current Liabilities	1,025		1,435
Noncurrent Liabilities	2,905		2,880
Long-Term Debt	2,137		2,136
Member's Equity	6,196		5,967
TOTAL LIABILITIES AND CAPITALIZATION	$ 12,263		$ 12,418