Segment Information

3 Months Ended

Mar. 31, 2013

Segment Reporting [Abstract]

SEGMENT INFORMATION

SEGMENT INFORMATION

Ameren historically had three reportable segments: Ameren Missouri, Ameren Illinois, and Merchant Generation. The Ameren Missouri segment for both Ameren and Ameren Missouri includes all the operations of Ameren Missouri’s business as described in Note 1 - Summary of Significant Accounting Policies. The Ameren Illinois segment for both Ameren and Ameren Illinois includes all of the operations of Ameren Illinois’ business as described in Note 1 - Summary of Significant Accounting Policies. The Merchant Generation segment for Ameren consisted primarily of the operations or activities of AER, including Genco, EEI, AERG, and Marketing Company. Ameren is divesting its Merchant Generation segment and therefore has excluded that segment’s information below. See Note 2 - Divestiture Transactions and Discontinued Operations for information regarding the Merchant Generation segment. The category called Other primarily includes Ameren parent company activities, Ameren Services, and ATXI. The Other category also includes activities previously included in the Merchant Generation segment that will be retained by Ameren after the divestiture of New AER and the sale of the Elgin, Gibson City, and Grand Tower gas-fired energy centers is complete. See Note 2 - Divestiture Transactions and Discontinued Operations for information regarding the assets and liabilities retained by Ameren after the divestitures.

The following table presents information about the revenues and specified items included in Ameren’s net income for the three months ended March 31, 2013, and 2012, and total assets as of March 31, 2013, and December 31, 2012.

Three Months	Ameren Missouri		Ameren Illinois		Other			Intersegment Eliminations			Consolidated
2013
External revenues	$	789	$	684	$	2		$	—		$	1,475
Intersegment revenues	7		—		2			(9		)	—
Net income (loss) attributable to Ameren Corporation from continuing operations	40		31		(17		)	—			54
2012
External revenues	$	686	$	724	$	2		$	—		$	1,412
Intersegment revenues	5		—		1			(6		)	—
Net income (loss) attributable to Ameren Corporation from continuing operations	21		27		(11		)	—			37
As of March 31, 2013:
Total assets	$	12,867	$	7,288	$	1,289		$	(992	)	$	20,452	(a)
As of December 31, 2012:
Total assets	$	13,043	$	7,282	$	1,228		$	(944	)	$	20,609	(a)

(a)    Excludes “Current assets of discontinued operations.” See Note 2 - Divestiture Transactions and Discontinued Operations for additional information.