Nuclear Decommissioning Trust Fund Investments (Tables)

12 Months Ended

Dec. 31, 2015

Nuclear Decommissioning Trust Fund Investments [Line Items]

Fair Value Of Securities In Nuclear Decommissioning Trust Fund

The following table presents the costs and fair values of investments in debt and equity securities in Ameren's and Ameren Missouri’s nuclear decommissioning trust fund at December 31, 2015 and 2014:

Security Type	Cost			Gross Unrealized Gain			Gross Unrealized Loss	Fair Value
2015
Debt securities	$	191		$	2	$	4	$	189
Equity securities	147			224			7	364
Cash	4			—			—	4
Other(a)	(1		)	—			—	(1		)
Total	$	341		$	226	$	11	$	556
2014
Debt securities	$	175		$	7	$	—	$	182
Equity securities	138			230			4	364
Cash	1			—			—	1
Other(a)	2			—			—	2
Total	$	316		$	237	$	4	$	549

(a) Represents payables relating to pending security purchases, net of receivables related to pending security sales and interest.

Schedule Of Unrealized Losses On Available-For-Sale Investments Included In Nuclear Decommissioning Trust Fund

The following table presents the fair value and the gross unrealized losses of the available-for-sale securities held in Ameren's and Ameren Missouri's nuclear decommissioning trust fund. They are aggregated by investment category and the length of time that individual securities have been in a continuous unrealized loss position at December 31, 2015:

	Less than 12 Months				12 Months or Greater				Total
	Fair Value			Gross Unrealized Losses	Fair Value			Gross Unrealized Losses	Fair Value			Gross Unrealized Losses
Debt securities	$	136	$	3	$	4	$	1	$	140	$	4
Equity securities	16			3	4			4	20			7
Total	$	152	$	6	$	8	$	5	$	160	$	11

Regulatory Asset

Nuclear Decommissioning Trust Fund Investments [Line Items]

Proceeds From Sale Of Investments In Nuclear Decommissioning Trust Fund And Gross Realized Gains And Losses

The following table presents proceeds from the sale and maturities of investments in Ameren Missouri’s nuclear decommissioning trust fund and the gross realized gains and losses resulting from those sales for the years ended December 31, 2015, 2014, and 2013:

	2015		2014		2013
Proceeds from sales and maturities	$	349	$	391	$	196
Gross realized gains	8		7		7
Gross realized losses	2		2		5

Fair Value Of Securities In Nuclear Decommissioning Trust Fund According To Their Contractual Maturities

The following table presents the costs and fair values of investments in debt securities in Ameren's and Ameren Missouri’s nuclear decommissioning trust fund according to their contractual maturities at December 31, 2015:

	Cost		Fair Value
Less than 5 years	$	106	$	105
5 years to 10 years	42		41
Due after 10 years	43		43
Total	$	191	$	189