Segment Information

We assess our business on a regional basis due to the effect on our financial performance of the differing characteristics of these regions, particularly with respect to competition, regulation and other factors affecting supply and demand. At September 30, 2017, our reportable segments were West (including geothermal), Texas and East (including Canada). The results of our retail subsidiaries are reflected in the segment which corresponds with the geographic area in which the retail sales occur. We continue to evaluate the optimal manner in which we assess our performance including our segments and future changes may result in changes to the composition of our geographic segments. Commodity Margin is a key operational measure reviewed by our chief operating decision maker to assess the performance of our segments. The tables below show our financial data for our segments for the periods indicated (in millions):



	Three Months Ended September 30, 2017
	West			Texas		East			Consolidation and Elimination			Total
Revenues from external customers	$	553		$	1,127	$	906		$	—		$	2,586
Intersegment revenues	2			4		2			(8		)	—
Total operating revenues	$	555		$	1,131	$	908		$	(8	)	$	2,586
Commodity Margin	$	327		$	201	$	336		$	—		$	864
Add: Mark-to-market commodity activity, net and other⁽¹⁾	(40		)	88		(39		)	(8		)	1
Less:
Plant operating expense	83			77		75			(7		)	228
Depreciation and amortization expense	63			61		55			—			179
Sales, general and other administrative expense	10			16		10			1			37
Other operating expenses	13			6		6			(2		)	23
Impairment losses	—			12		—			—			12
(Income) from unconsolidated subsidiaries	—			—		(7		)	—			(7		)
Income from operations	118			117		158			—			393
Interest expense												156
Debt extinguishment costs and other (income) expense, net												8
Income before income taxes												$	229



	Three Months Ended September 30, 2016
	West		Texas		East			Consolidation and Elimination			Total
Revenues from external customers	$	524	$	1,067	$	764		$	—		$	2,355
Intersegment revenues	1		3		2			(6		)	—
Total operating revenues	$	525	$	1,070	$	766		$	(6	)	$	2,355
Commodity Margin	$	298	$	198	$	324		$	—		$	820
Add: Mark-to-market commodity activity, net and other⁽¹⁾	11		110		(51		)	(7		)	63
Less:
Plant operating expense	79		65		78			(7		)	215
Depreciation and amortization expense	56		53		52			—			161
Sales, general and other administrative expense	9		13		12			(1		)	33
Other operating expenses	8		2		7			1			18
(Income) from unconsolidated subsidiaries	—		—		(6		)	—			(6		)
Income from operations	157		175		130			—			462
Interest expense											158
Other (income) expense, net											7
Income before income taxes											$	297



	Nine Months Ended September 30, 2017
	West			Texas			East			Consolidation and Elimination			Total
Revenues from external customers	$	1,666		$	2,723		$	2,562		$	—		$	6,951
Intersegment revenues	4			12			6			(22		)	—
Total operating revenues	$	1,670		$	2,735		$	2,568		$	(22	)	$	6,951
Commodity Margin	$	792		$	516		$	761		$	—		$	2,069
Add: Mark-to-market commodity activity, net and other⁽²⁾	(1		)	28			(65		)	(22		)	(60		)
Less:
Plant operating expense	291			282			260			(21		)	812
Depreciation and amortization expense	189			187			166			—			542
Sales, general and other administrative expense	31			54			31			1			117
Other operating expenses	30			12			23			(2		)	63
Impairment losses	28			13			—			—			41
(Gain) on sale of assets, net	—			—			(27		)	—			(27		)
(Income) from unconsolidated subsidiaries	—			—			(17		)	—			(17		)
Income (loss) from operations	222			(4		)	260			—			478
Interest expense													469
Debt extinguishment costs and other (income) expense, net													42
Loss before income taxes													$	(33	)



	Nine Months Ended September 30, 2016
	West			Texas		East			Consolidation and Elimination			Total
Revenues from external customers	$	1,159		$	2,129	$	1,846		$	—		$	5,134
Intersegment revenues	4			10		9			(23		)	—
Total operating revenues	$	1,163		$	2,139	$	1,855		$	(23	)	$	5,134
Commodity Margin	$	749		$	511	$	797		$	—		$	2,057
Add: Mark-to-market commodity activity, net and other⁽²⁾	(5		)	7		(44		)	(21		)	(63		)
Less:
Plant operating expense	268			236		258			(21		)	741
Depreciation and amortization expense	168			159		163			—			490
Sales, general and other administrative expense	27			43		36			—			106
Other operating expenses	23			6		27			(1		)	55
Impairment losses	13			—		—			—			13
(Income) from unconsolidated subsidiaries	—			—		(16		)	—			(16		)
Income from operations	245			74		285			1			605
Interest expense												472
Debt extinguishment costs and other (income) expense, net												33
Income before income taxes												$	100

_________


(1)	Includes $33 million and $40 million of lease levelization and $39 million and $25 million of amortization expense for the three months ended September 30, 2017 and 2016, respectively.


(2)	Includes $(13) million and $(2) million of lease levelization and $143 million and $79 million of amortization expense for the nine months ended September 30, 2017 and 2016, respectively.