Guarantees Of Debt (Schedule Of Financial Statements Of Guarantors) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Debt Instrument [Line Items]
Operating Revenues	$ 2,133	$ 1,905	$ 4,725	$ 4,521
Operating Expenses	1,937	1,558	4,351	3,347
Operating Income (Loss)	196	347	374	1,174
Equity Earnings (Losses) of Subsidiaries	5	4	8	6
Other Income	70	44	142	92
Other Deductions	(9)	(10)	(20)	(31)
Other-Than-Temporary Impairments	(3)	(10)	(4)	(20)
Interest Expense	(91)	(97)	(189)	(189)
Income Tax Benefit (Expense)	(59)	(91)	(88)	(374)
Net Income (Loss)	109	187	223	658
Net Cash Provided By (Used In) Operating Activities			1,756	1,722
Net Cash Provided By (Used In) Investing Activities			(1,989)	(2,004)
Net Cash Provided By (Used In) Financing Activities			240	536
Current Assets	3,188		3,188		$ 3,254
Property, Plant and Equipment, net	29,637		29,637		29,286
Noncurrent Assets	7,699		7,699		7,530
Total Assets	40,524		40,524		40,070
Current Liabilities	3,164		3,164		3,276
Noncurrent Liabilities	12,821		12,821		12,769
Long-Term Debt	11,621		11,621		10,895
Member's Equity	12,918		12,918		13,130
TOTAL LIABILITIES AND CAPITALIZATION	40,524		40,524		40,070
Power [Member]
Debt Instrument [Line Items]
Operating Revenues	929	714	2,213	2,027
Operating Expenses	1,116	726	2,703	1,696
Operating Income (Loss)	(187)	(12)	(490)	331
Equity Earnings (Losses) of Subsidiaries	5	4	8	6
Other Income	46	25	84	51
Other Deductions	(7)	(9)	(14)	(27)
Other-Than-Temporary Impairments	(3)	(10)	(4)	(20)
Interest Expense	(13)	(20)	(29)	(42)
Income Tax Benefit (Expense)	62	11	178	(118)
Net Income (Loss)	(97)	(11)	(267)	181
Net Cash Provided By (Used In) Operating Activities			932	917
Net Cash Provided By (Used In) Investing Activities			(735)	(1,607)
Net Cash Provided By (Used In) Financing Activities			(179)	694
Current Assets	1,382		1,382		1,460
Property, Plant and Equipment, net	7,826		7,826		8,520
Noncurrent Assets	2,411		2,411		2,213
Total Assets	11,619		11,619		12,193
Current Liabilities	679		679		680
Noncurrent Liabilities	3,160		3,160		3,332
Long-Term Debt	2,384		2,384		2,382
Member's Equity	5,396		5,396		5,799
TOTAL LIABILITIES AND CAPITALIZATION	11,619		11,619		12,193
Power Senior Notes [Member] | Consolidating Adjustments [Member]
Debt Instrument [Line Items]
Operating Revenues	(28)	(32)	(66)	(63)
Operating Expenses	(28)	(32)	(66)	(63)
Operating Income (Loss)	0	0	0	0
Equity Earnings (Losses) of Subsidiaries	97	0	259	(204)
Other Income	(34)	(22)	(62)	(45)
Other Deductions	0	0	0	0
Other-Than-Temporary Impairments	0	0	0	0
Interest Expense	34	22	62	45
Income Tax Benefit (Expense)	0	0	0	0
Net Income (Loss)	97	0	259	(204)
Comprehensive Income (Loss)	88	(9)	229	(229)
Net Cash Provided By (Used In) Operating Activities			51	(356)
Net Cash Provided By (Used In) Investing Activities			(1,355)	579
Net Cash Provided By (Used In) Financing Activities			1,304	(223)
Current Assets	(4,213)		(4,213)		(4,697)
Property, Plant and Equipment, net	0		0		0
Investment in Subsidiaries	(4,355)		(4,355)		(4,593)
Noncurrent Assets	(117)		(117)		(100)
Total Assets	(8,685)		(8,685)		(9,390)
Current Liabilities	(4,213)		(4,213)		(4,697)
Noncurrent Liabilities	(117)		(117)		(100)
Long-Term Debt	0		0		0
Member's Equity	(4,355)		(4,355)		(4,593)
TOTAL LIABILITIES AND CAPITALIZATION	(8,685)		(8,685)		(9,390)
Power Senior Notes [Member] | Power Parent [Member]
Debt Instrument [Line Items]
Operating Revenues	0	0	0	0
Operating Expenses	(2)	2	2	12
Operating Income (Loss)	2	(2)	(2)	(12)
Equity Earnings (Losses) of Subsidiaries	(93)	(1)	(254)	204
Other Income	22	17	47	34
Other Deductions	0	0	(1)	0
Other-Than-Temporary Impairments	0	0	0	0
Interest Expense	(34)	(31)	(64)	(61)
Income Tax Benefit (Expense)	6	6	7	16
Net Income (Loss)	(97)	(11)	(267)	181
Comprehensive Income (Loss)	(82)	5	(228)	220
Net Cash Provided By (Used In) Operating Activities			(32)	337
Net Cash Provided By (Used In) Investing Activities			683	(1,287)
Net Cash Provided By (Used In) Financing Activities			(651)	951
Current Assets	4,156		4,156		4,412
Property, Plant and Equipment, net	56		56		55
Investment in Subsidiaries	4,015		4,015		4,249
Noncurrent Assets	184		184		168
Total Assets	8,411		8,411		8,884
Current Liabilities	88		88		171
Noncurrent Liabilities	543		543		532
Long-Term Debt	2,384		2,384		2,382
Member's Equity	5,396		5,396		5,799
TOTAL LIABILITIES AND CAPITALIZATION	8,411		8,411		8,884
Power Senior Notes [Member] | Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	910	700	2,180	2,002
Operating Expenses	1,103	716	2,672	1,668
Operating Income (Loss)	(193)	(16)	(492)	334
Equity Earnings (Losses) of Subsidiaries	(4)	1	(5)	0
Other Income	56	30	97	62
Other Deductions	(7)	(9)	(13)	(27)
Other-Than-Temporary Impairments	(3)	(10)	(4)	(20)
Interest Expense	(9)	(7)	(18)	(17)
Income Tax Benefit (Expense)	60	3	171	(137)
Net Income (Loss)	(100)	(8)	(264)	195
Comprehensive Income (Loss)	(91)	1	(234)	220
Net Cash Provided By (Used In) Operating Activities			802	777
Net Cash Provided By (Used In) Investing Activities			178	(504)
Net Cash Provided By (Used In) Financing Activities			(978)	(273)
Current Assets	1,257		1,257		1,593
Property, Plant and Equipment, net	5,244		5,244		6,145
Investment in Subsidiaries	340		340		344
Noncurrent Assets	2,225		2,225		2,016
Total Assets	9,066		9,066		10,098
Current Liabilities	3,156		3,156		3,752
Noncurrent Liabilities	2,195		2,195		2,398
Long-Term Debt	0		0		0
Member's Equity	3,715		3,715		3,948
TOTAL LIABILITIES AND CAPITALIZATION	9,066		9,066		10,098
Power Senior Notes [Member] | Non-Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Operating Revenues	47	46	99	88
Operating Expenses	43	40	95	79
Operating Income (Loss)	4	6	4	9
Equity Earnings (Losses) of Subsidiaries	5	4	8	6
Other Income	2	0	2	0
Other Deductions	0	0	0	0
Other-Than-Temporary Impairments	0	0	0	0
Interest Expense	(4)	(4)	(9)	(9)
Income Tax Benefit (Expense)	(4)	2	0	3
Net Income (Loss)	3	8	5	9
Comprehensive Income (Loss)	3	8	5	9
Net Cash Provided By (Used In) Operating Activities			111	159
Net Cash Provided By (Used In) Investing Activities			(241)	(395)
Net Cash Provided By (Used In) Financing Activities			146	239
Current Assets	182		182		152
Property, Plant and Equipment, net	2,526		2,526		2,320
Investment in Subsidiaries	0		0		0
Noncurrent Assets	119		119		129
Total Assets	2,827		2,827		2,601
Current Liabilities	1,648		1,648		1,454
Noncurrent Liabilities	539		539		502
Long-Term Debt	0		0		0
Member's Equity	640		640		645
TOTAL LIABILITIES AND CAPITALIZATION	2,827		2,827		2,601
Power Senior Notes [Member] | Power [Member]
Debt Instrument [Line Items]
Operating Revenues	929	714	2,213	2,027
Operating Expenses	1,116	726	2,703	1,696
Operating Income (Loss)	(187)	(12)	(490)	331
Equity Earnings (Losses) of Subsidiaries	5	4	8	6
Other Income	46	25	84	51
Other Deductions	(7)	(9)	(14)	(27)
Other-Than-Temporary Impairments	(3)	(10)	(4)	(20)
Interest Expense	(13)	(20)	(29)	(42)
Income Tax Benefit (Expense)	62	11	178	(118)
Net Income (Loss)	(97)	(11)	(267)	181
Comprehensive Income (Loss)	(82)	$ 5	(228)	220
Net Cash Provided By (Used In) Operating Activities			932	917
Net Cash Provided By (Used In) Investing Activities			(735)	(1,607)
Net Cash Provided By (Used In) Financing Activities			(179)	$ 694
Current Assets	1,382		1,382		1,460
Property, Plant and Equipment, net	7,826		7,826		8,520
Investment in Subsidiaries	0		0		0
Noncurrent Assets	2,411		2,411		2,213
Total Assets	11,619		11,619		12,193
Current Liabilities	679		679		680
Noncurrent Liabilities	3,160		3,160		3,332
Long-Term Debt	2,384		2,384		2,382
Member's Equity	5,396		5,396		5,799
TOTAL LIABILITIES AND CAPITALIZATION	$ 11,619		$ 11,619		$ 12,193