Summary Of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Schedule Of Inventories

The following table presents a breakdown of inventories for each of the Ameren Companies at December 31, 2017 and 2016:

	Ameren Missouri		Ameren Illinois		Ameren
2017
Fuel(a)	$	154	$	—	$	154
Natural gas stored underground	8		74		82
Materials, supplies, and other	226		60		286
Total inventories	$	388	$	134	$	522
2016
Fuel(a)	$	172	$	—	$	172
Natural gas stored underground	9		73		82
Materials, supplies, and other	211		62		273
Total inventories	$	392	$	135	$	527

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

Schedule Of Rates Used For Allowance For Funds Used During Construction

The following table presents the annual allowance for funds used during construction debt and equity blended rates that were applied to construction projects in 2017, 2016, and 2015:

	2017		2016		2015
Ameren Missouri	7	%	7	%	7	%
Ameren Illinois	4	%	5	%	6	%

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, 2017 and 2016:

	Ameren Missouri				Ameren Illinois				Ameren
Balance at December 31, 2015	$	617			$	6			$	623
Liabilities incurred	3				—				3
Liabilities settled	(2		)		(a)				(2		)
Accretion in 2016(b)	25				(a)				25
Change in estimates	1				—				1
Balance at December 31, 2016	$	644		(c)	$	6		(d)	$	650		(c)
Liabilities incurred	—				—				—
Liabilities settled	(12		)		(1		)		(13		)
Accretion in 2017(b)	26				(a)				26
Change in estimates(e)	(18		)		(1		)		(19		)
Balance at December 31, 2017	$	640		(c)	$	4		(d)	$	644		(c)

(a) Less than $1 million.

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

(c) Balance included $6 million and $15 million in “Other current liabilities” on the balance sheet as of December 31, 2017 and 2016, respectively.

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

(e) 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.

Schedule Of Excise Taxes

The following table presents the excise taxes recorded in “Operating Revenues – Electric,” “Operating Revenues – Natural gas,” and “Operating Expenses – Taxes other than income taxes” for the years ended December 31, 2017, 2016, and 2015:

	2017		2016		2015
Ameren Missouri	$	153	$	151	$	156
Ameren Illinois	57		57		57
Ameren	$	210	$	208	$	213