Summary Of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Schedule of Cash and Cash Equivalents Including Restricted Cash [Table Text Block]

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets as of December 31, 2018and2017:

	December 31, 2018						December 31, 2017
	Ameren		Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois
Cash and cash equivalents	$	16	$	—	$	—	$	10	$	—	$	—
Restricted cash included in “Other current assets”	13		4		6		21		5		6
Restricted cash included in “Other assets”	74		—		74		35		—		35
Restricted cash included in “Nuclear decommissioning trust fund”	4		4		—		2		2		—
Total cash, cash equivalents, and restricted cash	$	107	$	8	$	80	$	68	$	7	$	41

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheet as of December 31, 2018and2017:

	2018		2017
Cash and cash equivalents	$	—	$	—
Restricted cash included in “Other current assets”	1		8
Total cash, cash equivalents, and restricted cash	$	1	$	8

Schedule Of Inventories

The following table presents a breakdown of inventories for each of the Ameren Companies at December 31, 2018 and 2017:

	Ameren Missouri		Ameren Illinois		Ameren
2018
Fuel(a)	$	123	$	—	$	123
Natural gas stored underground	7		64		71
Materials, supplies, and other	228		61		289
Total inventories	$	358	$	125	$	483
2017
Fuel(a)	$	154	$	—	$	154
Natural gas stored underground	8		74		82
Materials, supplies, and other	226		60		286
Total inventories	$	388	$	134	$	522

(a) Consists of coal, oil, and propane.

Schedule Of Rates Used For Allowance For Funds Used During Construction

The following table presents the average allowance for funds used during construction debt and equity blended rates that were applied to construction projects in 2018, 2017, and 2016:

	2018		2017		2016
Ameren Missouri	7	%	7	%	7	%
Ameren Illinois	5	%	4	%	5	%

Schedule Of Asset Retirement Obligations

The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the years ended December 31, 2018 and 2017:

	Ameren Missouri				Ameren Illinois				Ameren
Balance at December 31, 2016	$	644			$	6			$	650
Liabilities settled	(12		)		(1		)		(13		)
Accretion(a)	26				—				26
Change in estimates(b)	(18		)		(1		)		(19		)
Balance at December 31, 2017	$	640		(c)	$	4		(d)	$	644		(c)
Liabilities settled	(7		)		—				(7		)
Accretion(a)	27				—				27
Change in estimates(e)	(14		)		—				(14		)
Balance at December 31, 2018	$	646		(c)	$	4		(d)	$	650		(c)

(a) Ameren Missouri’s accretion expense was deferred as a decrease to regulatory liabilities.

(b) Ameren Missouri changed its fair value estimate primarily because of an extension of the remediation period of certain CCR storage facilities, an update to the decommissioning of the Callaway energy center to reflect the cost study and funding analysis filed with the MoPSC in 2017, and an increase in the assumed discount rate.

(c) Balance included $23 million and $6 million in “Other current liabilities” on the balance sheet as of December 31, 2018 and 2017, respectively.

(d) Included in “Other deferred credits and liabilities” on the balance sheet.

(e) Ameren Missouri changed its fair value estimate primarily due to a reduction in the cost estimate for closure of certain CCR storage facilities.

Schedule Of Excise Taxes

The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the years ended December 31, 2018, 2017, and 2016:

	2018		2017			2016
Ameren Missouri	$	164	$	153		$	151
Ameren Illinois	118		112		(a)	108		(a)
Ameren	$	282	$	265		$	259

(a) Amounts have been adjusted from those previously reported to reflect additional excise taxes for the years ended December 31, 2017 and 2016.