Guarantees Of Debt (Schedule Of Financial Statements Of Guarantors) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Operating Revenues	$ 3,135us-gaap_Revenues	$ 3,223us-gaap_Revenues
Operating Expenses	2,087us-gaap_OperatingExpenses	2,518us-gaap_OperatingExpenses
Operating Income (Loss)	1,048us-gaap_OperatingIncomeLoss	705us-gaap_OperatingIncomeLoss
Equity Earnings (Losses) of Subsidiaries	3	4
Other Income	48us-gaap_OtherNonoperatingIncome	48us-gaap_OtherNonoperatingIncome
Other Deductions	(12)us-gaap_OtherNonoperatingExpense	(12)us-gaap_OtherNonoperatingExpense
Other-Than Temporary Impairments	5	2
Interest Expense	(98)us-gaap_InterestExpense	(97)us-gaap_InterestExpense
Income Tax Expense	(398)us-gaap_IncomeTaxExpenseBenefit	(260)us-gaap_IncomeTaxExpenseBenefit
Net Income	586us-gaap_NetIncomeLoss	386us-gaap_NetIncomeLoss
Net Cash Provided By (Used In) Operating Activities	1,679	1,116
Net Cash Provided By (Used In) Investing Activities	(779)	(629)
Net Cash Provided By (Used In) Financing Activities	(294)	(325)
Current Assets	4,159us-gaap_AssetsCurrent		4,119us-gaap_AssetsCurrent
Property, Plant and Equipment, net	23,978		23,589
Noncurrent Assets	7,690us-gaap_AssetsNoncurrent		7,625us-gaap_AssetsNoncurrent
Total Assets	35,827us-gaap_Assets		35,333us-gaap_Assets
Current Liabilities	3,622us-gaap_LiabilitiesCurrent		3,478us-gaap_LiabilitiesCurrent
Noncurrent Liabilities	11,557us-gaap_LiabilitiesNoncurrent		11,408us-gaap_LiabilitiesNoncurrent
Long-Term Debt	8,090us-gaap_LongTermDebtNoncurrent		8,261us-gaap_LongTermDebtNoncurrent
Member's Equity	12,558		12,186
TOTAL LIABILITIES AND CAPITALIZATION	35,827		35,333
Power Senior Notes [Member]
Operating Revenues	1,725	1,700
Operating Expenses	1,141	1,418
Operating Income (Loss)	584	282
Equity Earnings (Losses) of Subsidiaries	3	4
Other Income	29	33
Other Deductions	(11)	(10)
Other-Than Temporary Impairments	5	2
Interest Expense	(31)	(32)
Income Tax Expense	(234)	(111)
Net Income	335	164
Comprehensive Income (Loss)	347	170
Net Cash Provided By (Used In) Operating Activities	850	674
Net Cash Provided By (Used In) Investing Activities	(635)	(295)
Net Cash Provided By (Used In) Financing Activities	(200)	(375)
Current Assets	2,482		2,359
Property, Plant and Equipment, net	7,477		7,515
Investment in Subsidiaries	0		0
Noncurrent Assets	2,261		2,172
Total Assets	12,220		12,046
Current Liabilities	1,131		1,184
Noncurrent Liabilities	3,140		3,061
Long-Term Debt	2,244		2,243
Member's Equity	5,705		5,558
TOTAL LIABILITIES AND CAPITALIZATION	12,220		12,046
Power Senior Notes [Member] \| Guarantor Subsidiaries [Member]
Operating Revenues	1,715	1,684
Operating Expenses	1,131	1,404
Operating Income (Loss)	584	280
Equity Earnings (Losses) of Subsidiaries	(1)	0
Other Income	30	33
Other Deductions	(11)	(6)
Other-Than Temporary Impairments	5	2
Interest Expense	(9)	(7)
Income Tax Expense	(242)	(125)
Net Income	346	173
Comprehensive Income (Loss)	351	176
Net Cash Provided By (Used In) Operating Activities	772	603
Net Cash Provided By (Used In) Investing Activities	(515)	(315)
Net Cash Provided By (Used In) Financing Activities	(242)	(287)
Current Assets	1,835		2,037
Property, Plant and Equipment, net	6,230		6,265
Investment in Subsidiaries	118		120
Noncurrent Assets	2,035		1,952
Total Assets	10,218		10,374
Current Liabilities	3,313		3,606
Noncurrent Liabilities	2,529		2,442
Long-Term Debt	0		0
Member's Equity	4,376		4,326
TOTAL LIABILITIES AND CAPITALIZATION	10,218		10,374
Power Senior Notes [Member] \| Power Parent [Member]
Operating Revenues	0	0
Operating Expenses	5	4
Operating Income (Loss)	(5)	(4)
Equity Earnings (Losses) of Subsidiaries	349	177
Other Income	11	8
Other Deductions	0	(4)
Other-Than Temporary Impairments	0	0
Interest Expense	(29)	(28)
Income Tax Expense	9	15
Net Income	335	164
Comprehensive Income (Loss)	347	170
Net Cash Provided By (Used In) Operating Activities	327	291
Net Cash Provided By (Used In) Investing Activities	(537)	(122)
Net Cash Provided By (Used In) Financing Activities	210	(166)
Current Assets	4,554		4,263
Property, Plant and Equipment, net	79		81
Investment in Subsidiaries	4,571		4,516
Noncurrent Assets	287		278
Total Assets	9,491		9,138
Current Liabilities	1,093		883
Noncurrent Liabilities	449		454
Long-Term Debt	2,244		2,243
Member's Equity	5,705		5,558
TOTAL LIABILITIES AND CAPITALIZATION	9,491		9,138
Power Senior Notes [Member] \| Consolidating Adjustments [Member]
Operating Revenues	(58)	(24)
Operating Expenses	(58)	(24)
Operating Income (Loss)	0	0
Equity Earnings (Losses) of Subsidiaries	(348)	(177)
Other Income	(12)	(8)
Other Deductions	0	0
Other-Than Temporary Impairments	0	0
Interest Expense	12	8
Income Tax Expense	0	0
Net Income	(348)	(177)
Comprehensive Income (Loss)	(353)	(180)
Net Cash Provided By (Used In) Operating Activities	(260)	(221)
Net Cash Provided By (Used In) Investing Activities	430	142
Net Cash Provided By (Used In) Financing Activities	(170)	79
Current Assets	(4,043)		(4,091)
Property, Plant and Equipment, net	0		0
Investment in Subsidiaries	(4,689)		(4,636)
Noncurrent Assets	(197)		(195)
Total Assets	(8,929)		(8,922)
Current Liabilities	(4,043)		(4,091)
Noncurrent Liabilities	(197)		(195)
Long-Term Debt	0		0
Member's Equity	(4,689)		(4,636)
TOTAL LIABILITIES AND CAPITALIZATION	(8,929)		(8,922)
Power Senior Notes [Member] \| Non-Guarantor Subsidiaries [Member]
Operating Revenues	68	40
Operating Expenses	63	34
Operating Income (Loss)	5	6
Equity Earnings (Losses) of Subsidiaries	3	4
Other Income	0	0
Other Deductions	0	0
Other-Than Temporary Impairments	0	0
Interest Expense	(5)	(5)
Income Tax Expense	(1)	(1)
Net Income	2	4
Comprehensive Income (Loss)	2	4
Net Cash Provided By (Used In) Operating Activities	11	1
Net Cash Provided By (Used In) Investing Activities	(13)	0
Net Cash Provided By (Used In) Financing Activities	2	(1)
Current Assets	136		150
Property, Plant and Equipment, net	1,168		1,169
Investment in Subsidiaries	0		0
Noncurrent Assets	136		137
Total Assets	1,440		1,456
Current Liabilities	768		786
Noncurrent Liabilities	359		360
Long-Term Debt	0		0
Member's Equity	313		310
TOTAL LIABILITIES AND CAPITALIZATION	1,440		1,456
Increase (Decrease) from Previously Reported \| Power Senior Notes [Member]
Operating Revenues		0
Operating Expenses		0
Net Cash Provided By (Used In) Investing Activities		0
Net Cash Provided By (Used In) Financing Activities		0
Increase (Decrease) from Previously Reported \| Power Senior Notes [Member] \| Guarantor Subsidiaries [Member]
Operating Revenues		(393)
Operating Expenses		(393)
Net Cash Provided By (Used In) Investing Activities		0
Net Cash Provided By (Used In) Financing Activities		0
Increase (Decrease) from Previously Reported \| Power Senior Notes [Member] \| Power Parent [Member]
Operating Revenues		0
Operating Expenses		0
Net Cash Provided By (Used In) Investing Activities		(209)
Net Cash Provided By (Used In) Financing Activities		209
Increase (Decrease) from Previously Reported \| Power Senior Notes [Member] \| Consolidating Adjustments [Member]
Operating Revenues		393
Operating Expenses		393
Net Cash Provided By (Used In) Investing Activities		209
Net Cash Provided By (Used In) Financing Activities		(209)
Increase (Decrease) from Previously Reported \| Power Senior Notes [Member] \| Non-Guarantor Subsidiaries [Member]
Operating Revenues		0
Operating Expenses		0
Net Cash Provided By (Used In) Investing Activities		0
Net Cash Provided By (Used In) Financing Activities		$ 0

Guarantees Of Debt (Schedule Of Financial Statements Of Guarantors) (Detail) (USD $)
In Millions, unless otherwise specified

3 Months Ended

Mar. 31, 2015

Mar. 31, 2014

Dec. 31, 2014

Operating Income (Loss)