Segment Information

12 Months Ended

Dec. 31, 2017

Segment Reporting Information, Profit (Loss) [Abstract]

SEGMENT INFORMATION

SEGMENT INFORMATION

Ameren 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. 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, Ameren Illinois, and ATXI.

Segment operating revenues and a majority of operating expenses are directly recognized and incurred by Ameren Illinois to each Ameren Illinois segment. Common operating expenses, miscellaneous income and expenses, 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 and wholesale customers. 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 in Ameren Transmission’s and Ameren Illinois Transmission’s operating revenues. An intersegment elimination at Ameren and Ameren Illinois occurs to eliminate these transmission revenues and expenses.

The following tables present revenues, net income attributable to common shareholders, and capital expenditures by segment at Ameren and Ameren Illinois for the years ended December 31, 2017, 2016, and 2015. 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
2017
External revenues	$	3,490	$	1,565	$	742	$	382		$	(2	)	$	—		$	6,177
Intersegment revenues	49		4		1		44		(a)	—			(98		)	—
Depreciation and amortization	533		239		59		60			5			—			896
Interest income	27		7		—		—			11			(11		)	34
Interest charges	207		73		36		67		(b)	19			(11		)	391
Income taxes	254		83		36		90			113			—			576
Net income (loss) attributable to Ameren common shareholders from continuing operations	323		131		60		140			(131		)	—			523
Capital expenditures	773		476		245		644			1			(7		)	2,132
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		(b)	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			(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		(b)	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			—			1,917

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

(b) Ameren Transmission interest charges include an allocation of financing costs from Ameren (parent).

Ameren Illinois

	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission			Intersegment Eliminations			Consolidated
2017
External revenues	$	1,569	$	743	$	216		$	—		$	2,528
Intersegment revenues	—		—		42		(a)	(42		)	—
Depreciation and amortization	239		59		43			—			341
Interest income	7		—		—			—			7
Interest charges	73		36		35			—			144
Income taxes	83		36		47			—			166
Net income available to common shareholder	131		60		77			—			268
Capital expenditures	476		245		355			—			1,076
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

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