Segment and Significant Customer Information (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenues		$ 2,082	$ 2,792	$ 2,599	$ 2,599	$ 2,354	$ 2,890	$ 2,259	$ 2,009	$ 10,072	[1]	$ 9,512	[1]	$ 8,752	[1]
Commodity Margin										3,314		3,033		2,708
Mark-to-Market Commodity Activity, Net and Other Revenue	[2]									254		(270)		(294)
Operating and maintenance expense										1,001		1,020		1,080
Depreciation and amortization expense										694		739		724
General and other administrative expense										150		158		155
Other Cost and Expense, Operating										79		98		85
Impairment losses										84		10		41
(Gain) on sale of assets, net										(10)		0		(27)
(Income) from unconsolidated subsidiaries										22		24		22
Income from operations		$ 108	$ 682	$ 444	$ 358	$ 105	$ 568	$ 417	$ (328)	1,592		762		378
Interest expense, net of interest income										609		617		621
Debt Extinguishment Costs and Other (Income) Expense, Net										95		53		70
Income before income taxes										888		92		(313)
Lease levelization										1		0		(8)
Contract amortization										$ 72		$ 100		$ 175
Number of significant customers										0		0		0
West [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenues	[1]									$ 2,743		$ 1,988		$ 1,881
Commodity Margin										1,151		1,060		970
Mark-to-Market Commodity Activity, Net and Other Revenue	[2]									219		(165)		(19)
Operating and maintenance expense										340		348		361
Depreciation and amortization expense										254		269		240
General and other administrative expense										35		40		45
Other Cost and Expense, Operating										31		42		38
Impairment losses										0		0		28
(Gain) on sale of assets, net										(4)				0
(Income) from unconsolidated subsidiaries										0		0		0
Income from operations										714		196		239
Texas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenues	[1]									3,081		2,860		2,342
Commodity Margin										857		646		552
Mark-to-Market Commodity Activity, Net and Other Revenue	[2]									154		(197)		(174)
Operating and maintenance expense										269		272		308
Depreciation and amortization expense										196		237		208
General and other administrative expense										53		61		66
Other Cost and Expense, Operating										6		24		14
Impairment losses										13		0		13
(Gain) on sale of assets, net										0				0
(Income) from unconsolidated subsidiaries										0		0		0
Income from operations										474		(145)		(231)
East [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenues	[1]									2,164		1,987		1,658
Commodity Margin										924		970		790
Mark-to-Market Commodity Activity, Net and Other Revenue	[2]									46		40		(62)
Operating and maintenance expense										278		269		302
Depreciation and amortization expense										191		180		201
General and other administrative expense										45		38		27
Other Cost and Expense, Operating										42		32		33
Impairment losses										71		10		0
(Gain) on sale of assets, net										(6)				(27)
(Income) from unconsolidated subsidiaries										24		26		24
Income from operations										373		507		216
Consolidation, Eliminations [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenues	[1]									(2,009)		(1,299)		(926)
Commodity Margin										0		0		0
Mark-to-Market Commodity Activity, Net and Other Revenue										(34)	[2]	(32)		(29)
Operating and maintenance expense										(34)		(32)		(29)
Depreciation and amortization expense										0		0		0
General and other administrative expense										0		0		0
Other Cost and Expense, Operating										0		0		0
Impairment losses										0		0		0
(Gain) on sale of assets, net										0				0
(Income) from unconsolidated subsidiaries										0		0		0
Income from operations										0		0		0
Retail [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenues	[1]									4,093		3,976		3,797
Commodity Margin										382		357		396
Mark-to-Market Commodity Activity, Net and Other Revenue										(131)	[2]	84		(10)
Operating and maintenance expense										148		163		138
Depreciation and amortization expense										53		53		75
General and other administrative expense										17		19		17
Other Cost and Expense, Operating										0		0		0
Impairment losses										0		0		0
(Gain) on sale of assets, net										0				0
(Income) from unconsolidated subsidiaries										(2)		(2)		(2)
Income from operations										31		204		154
Intersegment Eliminations [Member] | West [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenues										530		488		324
Intersegment Eliminations [Member] | Texas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenues										946		573		361
Intersegment Eliminations [Member] | East [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenues										522		234		237
Intersegment Eliminations [Member] | Retail [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenues										11		4		4
Other Assets [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Contract amortization										$ 78		$ 104		$ 178

[1] Includes intersegment revenues of $530 million, $488 million and $324 million in the West, $946 million, $573 million and $361 million in Texas, $522 million, $234 million and $237 million in the East and $11 million, $4 million, $4 million in Retail for the years ended December 31, 2019, 2018 and 2017, respectively.

[2] Includes $1 million, nil and $(8) million of lease levelization and $78 million, $104 million and $178 million of amortization expense for the years ended December 31, 2019, 2018 and 2017, respectively.