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