Guarantees Of Debt (Schedule Of Financial Statements Of Guarantors) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Debt Instrument [Line Items]
Operating Revenues	$ 2,592	$ 2,616
Operating Expenses	2,414	1,789
Operating Income (Loss)	178	827
Equity Earnings (Losses) of Subsidiaries	3	2
Other Income	72	48
Other Deductions	(11)	(21)
Other-Than-Temporary Impairments	(1)	(10)
Interest Expense	(98)	(92)
Income Tax Benefit (Expense)	(29)	(283)
Net Income (Loss)	114	471
Net Cash Provided By (Used In) Operating Activities	1,196	1,214
Net Cash Provided By (Used In) Investing Activities	(1,079)	(1,081)
Net Cash Provided By (Used In) Financing Activities	(347)	65
Current Assets	2,716		$ 3,254
Property, Plant and Equipment, net	29,345		29,286
Noncurrent Assets	7,603		7,530
Total Assets	39,664		40,070
Current Liabilities	3,111		3,276
Noncurrent Liabilities	12,650		12,769
Long-Term Debt	10,898		10,895
Member's Equity	13,005		13,130
TOTAL LIABILITIES AND CAPITALIZATION	39,664		40,070
Power [Member]
Debt Instrument [Line Items]
Operating Revenues	1,284	1,313
Operating Expenses	1,587	970
Operating Income (Loss)	(303)	343
Equity Earnings (Losses) of Subsidiaries	3	2
Other Income	38	26
Other Deductions	(7)	(18)
Other-Than-Temporary Impairments	(1)	(10)
Interest Expense	(16)	(22)
Income Tax Benefit (Expense)	116	(129)
Net Income (Loss)	(170)	192
Net Cash Provided By (Used In) Operating Activities	580	663
Net Cash Provided By (Used In) Investing Activities	(394)	(659)
Net Cash Provided By (Used In) Financing Activities	(179)	0
Current Assets	1,292		1,460
Property, Plant and Equipment, net	8,085		8,520
Noncurrent Assets	2,352		2,213
Total Assets	11,729		12,193
Current Liabilities	745		680
Noncurrent Liabilities	3,123		3,332
Long-Term Debt	2,383		2,382
Member's Equity	5,478		5,799
TOTAL LIABILITIES AND CAPITALIZATION	11,729		12,193
Power Senior Notes [Member] | Consolidating Adjustments [Member]
Debt Instrument [Line Items]
Operating Revenues	(38)	(31)
Operating Expenses	(38)	(31)
Operating Income (Loss)	0	0
Equity Earnings (Losses) of Subsidiaries	162	(204)
Other Income	(28)	(23)
Other Deductions	0	0
Other-Than-Temporary Impairments	0	0
Interest Expense	28	23
Income Tax Benefit (Expense)	0	0
Net Income (Loss)	162	(204)
Comprehensive Income (Loss)	141	(220)
Net Cash Provided By (Used In) Operating Activities	35	(135)
Net Cash Provided By (Used In) Investing Activities	(511)	613
Net Cash Provided By (Used In) Financing Activities	476	(478)
Current Assets	(4,458)		(4,697)
Property, Plant and Equipment, net	0		0
Investment in Subsidiaries	(4,447)		(4,593)
Noncurrent Assets	(106)		(100)
Total Assets	(9,011)		(9,390)
Current Liabilities	(4,458)		(4,697)
Noncurrent Liabilities	(106)		(100)
Long-Term Debt	0		0
Member's Equity	(4,447)		(4,593)
TOTAL LIABILITIES AND CAPITALIZATION	(9,011)		(9,390)
Power Senior Notes [Member] | Power Parent [Member]
Debt Instrument [Line Items]
Operating Revenues	0	0
Operating Expenses	4	10
Operating Income (Loss)	(4)	(10)
Equity Earnings (Losses) of Subsidiaries	(161)	205
Other Income	25	17
Other Deductions	(1)	0
Other-Than-Temporary Impairments	0	0
Interest Expense	(30)	(30)
Income Tax Benefit (Expense)	1	10
Net Income (Loss)	(170)	192
Comprehensive Income (Loss)	(146)	215
Net Cash Provided By (Used In) Operating Activities	77	271
Net Cash Provided By (Used In) Investing Activities	251	(598)
Net Cash Provided By (Used In) Financing Activities	(328)	326
Current Assets	4,244		4,412
Property, Plant and Equipment, net	56		55
Investment in Subsidiaries	4,104		4,249
Noncurrent Assets	175		168
Total Assets	8,579		8,884
Current Liabilities	187		171
Noncurrent Liabilities	531		532
Long-Term Debt	2,383		2,382
Member's Equity	5,478		5,799
TOTAL LIABILITIES AND CAPITALIZATION	8,579		8,884
Power Senior Notes [Member] | Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	1,270	1,302
Operating Expenses	1,569	952
Operating Income (Loss)	(299)	350
Equity Earnings (Losses) of Subsidiaries	(1)	(1)
Other Income	41	32
Other Deductions	(6)	(18)
Other-Than-Temporary Impairments	(1)	(10)
Interest Expense	(9)	(10)
Income Tax Benefit (Expense)	111	(140)
Net Income (Loss)	(164)	203
Comprehensive Income (Loss)	(143)	219
Net Cash Provided By (Used In) Operating Activities	377	480
Net Cash Provided By (Used In) Investing Activities	20	(428)
Net Cash Provided By (Used In) Financing Activities	(395)	(51)
Current Assets	1,332		1,593
Property, Plant and Equipment, net	5,582		6,145
Investment in Subsidiaries	343		344
Noncurrent Assets	2,154		2,016
Total Assets	9,411		10,098
Current Liabilities	3,436		3,752
Noncurrent Liabilities	2,171		2,398
Long-Term Debt	0		0
Member's Equity	3,804		3,948
TOTAL LIABILITIES AND CAPITALIZATION	9,411		10,098
Power Senior Notes [Member] | Non-Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	52	42
Operating Expenses	52	39
Operating Income (Loss)	0	3
Equity Earnings (Losses) of Subsidiaries	3	2
Other Income	0	0
Other Deductions	0	0
Other-Than-Temporary Impairments	0	0
Interest Expense	(5)	(5)
Income Tax Benefit (Expense)	4	1
Net Income (Loss)	2	1
Comprehensive Income (Loss)	2	1
Net Cash Provided By (Used In) Operating Activities	91	47
Net Cash Provided By (Used In) Investing Activities	(154)	(246)
Net Cash Provided By (Used In) Financing Activities	68	203
Current Assets	174		152
Property, Plant and Equipment, net	2,447		2,320
Investment in Subsidiaries	0		0
Noncurrent Assets	129		129
Total Assets	2,750		2,601
Current Liabilities	1,580		1,454
Noncurrent Liabilities	527		502
Long-Term Debt	0		0
Member's Equity	643		645
TOTAL LIABILITIES AND CAPITALIZATION	2,750		2,601
Power Senior Notes [Member] | Power [Member]
Debt Instrument [Line Items]
Operating Revenues	1,284	1,313
Operating Expenses	1,587	970
Operating Income (Loss)	(303)	343
Equity Earnings (Losses) of Subsidiaries	3	2
Other Income	38	26
Other Deductions	(7)	(18)
Other-Than-Temporary Impairments	(1)	(10)
Interest Expense	(16)	(22)
Income Tax Benefit (Expense)	116	(129)
Net Income (Loss)	(170)	192
Comprehensive Income (Loss)	(146)	215
Net Cash Provided By (Used In) Operating Activities	580	663
Net Cash Provided By (Used In) Investing Activities	(394)	(659)
Net Cash Provided By (Used In) Financing Activities	(179)	$ 0
Current Assets	1,292		1,460
Property, Plant and Equipment, net	8,085		8,520
Investment in Subsidiaries	0		0
Noncurrent Assets	2,352		2,213
Total Assets	11,729		12,193
Current Liabilities	745		680
Noncurrent Liabilities	3,123		3,332
Long-Term Debt	2,383		2,382
Member's Equity	5,478		5,799
TOTAL LIABILITIES AND CAPITALIZATION	$ 11,729		$ 12,193