Segment Information

12 Months Ended

Dec. 31, 2016

Segment Reporting Information, Profit (Loss) [Abstract]

SEGMENT INFORMATION

SEGMENT INFORMATION

During the fourth quarter of 2016, the Ameren Companies changed the manner in which performance is assessed and resources are allocated, driven by increasing investment in FERC-regulated electric transmission and Ameren Illinois electric distribution and natural gas distribution businesses, as well as the unique regulatory environment for each jurisdiction. Ameren now has four segments: Ameren Missouri, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Transmission. The Ameren Missouri segment includes all of the operations of Ameren Missouri. Ameren Illinois Electric Distribution consists of the electric distribution business of Ameren Illinois. Ameren Illinois Natural Gas consists of the natural gas business of Ameren Illinois. Ameren Transmission is primarily composed of the aggregated electric transmission businesses of Ameren Illinois and ATXI and associated Ameren (parent) interest charges. The category called Other primarily includes Ameren parent company activities and Ameren Services.

Ameren Missouri has one segment. Ameren Illinois hasthreesegments: Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission. See Note 1 – Summary of Significant Accounting Policies for additional information regarding the operations of Ameren Missouri and Ameren Illinois.

Segment operating revenue and a majority of operating expenses are directly assigned by Ameren Illinois to each Ameren Illinois segment. Common operating expenses, miscellaneous income and expense, interest charges, and income tax expense are allocated by Ameren Illinois to each Ameren Illinois segment based on certain factors, which primarily relate to the nature of the cost. Additionally, Ameren Illinois Transmission earns revenue from transmission service provided to Ameren Illinois Electric Distribution. The transmission expense for Illinois customers who have elected to purchase their power from Ameren Illinois is recovered through a cost recovery mechanism with no net effect on Ameren Illinois Electric Distribution earnings, as costs are offset by corresponding revenues. Transmission revenues from these transactions are reflected at Ameren Transmission and Ameren Illinois Transmission. An intersegment elimination at Ameren and Ameren Illinois occurs to eliminate these transmission revenues and expenses.

Prior to the fourth quarter of 2016, Ameren had two segments: Ameren Missouri and Ameren Illinois, which comprised the operations of the respective subsidiaries. The category called Other primarily included Ameren parent company activities, Ameren Services, and ATXI. Prior-period presentation has been adjusted for comparative purposes to reflect the 2016 change in segments.

The following tables present information about the reported revenues and specified items reflected in net income attributable to common shareholders from continuing operations and capital expenditures at Ameren and Ameren Illinois for the years ended December 31, 2016, 2015, and 2014. Ameren, Ameren Missouri, and Ameren Illinois management review segment capital expenditure information rather than any individual or total asset amount.

Ameren

	Ameren Missouri		Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission			Other				Intersegment Eliminations			Consolidated
2016
External revenues	$	3,469	$	1,545	$	753	$	309		$	—			$	—		$	6,076
Intersegment revenues	54		4		1		46		(a)	—				(105		)	—
Depreciation and amortization	514		226		55		43			7				—			845
Interest income	28		11		—		1			11				(11		)	40
Interest charges	211		72		34		58			18				(11		)	382
Income taxes	216		78		39		74			(25		)		—			382
Net income (loss) attributable to Ameren common shareholders from continuing operations	357		126		59		117			(6		)		—			653
Capital expenditures	738		470		181		689			4			(b)	(6		)	2,076
2015
External revenues	$	3,566	$	1,529	$	782	$	219		$	2			$	—		$	6,098
Intersegment revenues	43		3		1		40		(a)	—				(87		)	—
Depreciation and amortization	492		212		52		33			7				—			796
Interest income	28		12		—		—			7				(6		)	41
Interest charges	219		71		35		35			1				(6		)	355
Income taxes	209		71		24		51			8				—			363
Net income (loss) attributable to Ameren common shareholders from continuing operations	352		123		37		83			(16		)		—			579
Capital expenditures	622		491		133		669			2			(b)	—			1,917
2014
External revenues	$	3,526	$	1,401	$	976	$	150		$	—			$	—		$	6,053
Intersegment revenues	27		2		—		37		(a)	—				(66		)	—
Depreciation and amortization	473		197		41		26			8				—			745
Interest income	28		7		—		—			5				(3		)	37
Interest charges	211		63		28		26			16				(3		)	341
Income taxes	229		75		39		38			(4		)		—			377
Net income (loss) attributable to Ameren common shareholders from continuing operations	390		113		50		51			(17		)		—			587
Capital expenditures	747		403		137		491			7			(b)	—			1,785

(a) Ameren Illinois Transmission earns revenue from transmission service provided to Ameren Illinois Electric Distribution. See discussion of transactions above.

(b) Includes the elimination of intercompany transfers.    

Ameren Illinois

	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission			Intersegment Eliminations			Consolidated
2016
External revenues	$	1,549	$	754	$	187		$	—		$	2,490
Intersegment revenues	—		—		45		(a)	(45		)	—
Depreciation and amortization	226		55		38			—			319
Interest income	11		—		1			—			12
Interest charges	72		34		34			—			140
Income taxes	78		39		41			—			158
Net income available to common shareholder	126		59		67			—			252
Capital expenditures	470		181		273			—			924
2015
External revenues	$	1,532	$	783	$	151		$	—		$	2,466
Intersegment revenues	—		—		38		(a)	(38		)	—
Depreciation and amortization	212		52		31			—			295
Interest income	12		—		—			—			12
Interest charges	71		35		25			—			131
Income taxes	71		24		32			—			127
Net income available to common shareholder	123		37		54			—			214
Capital expenditures	491		133		294			—			918
2014
External revenues	$	1,403	$	976	$	119		$	—		$	2,498
Intersegment revenues	—		—		35		(a)	(35		)	—
Depreciation and amortization	197		41		25			—			263
Interest income	7		—		—			—			7
Interest charges	63		28		21			—			112
Income taxes	75		39		29			—			143
Net income available to common shareholder	113		50		38			—			201
Capital expenditures	403		137		295			—			835

(a) Ameren Illinois Transmission earns revenue from transmission service provided to Ameren Illinois Electric Distribution. See discussion of transactions above.