The following table presents our regulatory assets and regulatory liabilities at December 31, 2015 and 2014:



	2015						2014
	Ameren Missouri		Ameren Illinois		Ameren			Ameren Missouri		Ameren Illinois		Ameren
Current regulatory assets:
Under-recovered FAC^(a)(b)	$	37	$	—	$	37		$	128	$	—	$	128
Under-recovered Illinois electric power costs^(c)	—		3		3			—		2		2
Under-recovered PGA^(c)	—		8		8			—		20		20
MTM derivative losses^(d)	29		45		74			32		42		74
Energy efficiency riders^(e)	23		—		23			3		—		3
IEIMA revenue requirement reconciliation adjustment^(a)(f)	—		103		103			—		65		65
FERC revenue requirement reconciliation adjustment^(a)(g)	—		8		12			—		—		3
Total current regulatory assets	$	89	$	167	$	260		$	163	$	129	$	295
Noncurrent regulatory assets:
Pension and postretirement benefit costs^(h)	$	95	$	202	$	297		$	148	$	275	$	423
Income taxes⁽ⁱ⁾	254		4		258			253		3		256
Asset retirement obligations^(j)	—		4		4			—		5		5
Callaway costs^(a)(k)	32		—		32			36		—		36
Unamortized loss on reacquired debt^(a)(l)	69		69		138			72		80		152
Contaminated facilities costs^(m)	—		230		230			—		251		251
MTM derivative losses^(d)	15		175		190			14		144		158
Storm costs^(a)(n)	—		9		9			—		3		3
Demand-side costs before the MEEIA implementation^(a)(o)	31		—		31			44		—		44
Workers’ compensation claims^(p)	6		7		13			7		7		14
Credit facilities fees^(q)	4		—		4			5		—		5
Construction accounting for pollution control equipment^(a)(r)	20		—		20			21		—		21
Solar rebate program^(a)(s)	74		—		74			88		—		88
IEIMA revenue requirement reconciliation adjustment^(a)(f)	—		62		62			—		101		101
FERC revenue requirement reconciliation adjustment^(a)(g)	—		5		11			—		8		12
Other	5		4		9			7		6		13
Total noncurrent regulatory assets	$	605	$	771	$	1,382		$	695	$	883	$	1,582
Current regulatory liabilities:
Over-recovered FAC^(b)	$	9	$	—	$	9		$	—	$	—	$	—
Over-recovered Illinois electric power costs^(c)	—		6		6			—		26		26
Over-recovered PGA^(c)	3		—		3			2		25		27
MTM derivative gains^(d)	16		1		17			16		1		17
FERC revenue requirement reconciliation adjustment^(g)	—		—		—			—		11		11
Estimated refund for FERC complaint cases, orders, and audit findings^(t)	—		32		45			—		21		25
Total current regulatory liabilities	$	28	$	39	$	80		$	18	$	84	$	106
Noncurrent regulatory liabilities:
Income taxes^(u)	$	36	$	6	$	42		$	41	$	14	$	55
Uncertain tax positions tracker^(v)	6		—		6			7		—		7
Removal costs^(w)	933		671		1,605			886		643		1,529
Asset retirement obligation^(j)	167		—		167			182		—		182
Bad debt riders^(x)	—		6		6			—		7		7
Pension and postretirement benefit costs tracker^(y)	19		—		19			24		—		24
Energy efficiency riders^(e)	—		36		36			—		39		39
Renewable energy credits^(z)	—		12		12			1		—		1
Storm tracker^(aa)	9		—		9			6		—		6
Other	2		1		3			—		—		—
Total noncurrent regulatory liabilities	$	1,172	$	732	$	1,905		$	1,147	$	703	$	1,850


(a)	These assets earn a return.


(b)	Under-recovered or over-recovered fuel costs to be recovered or refunded through the FAC. Specific accumulation periods aggregate the under-recovered or over-recovered costs over four months, any related adjustments that occur over the following four months, and the recovery from or refund to customers that occurs over the next eight months.


(c)	Under-recovered or over-recovered costs from utility customers. Amounts will be recovered from, or refunded to, customers within one year of the deferral.


(d)	Deferral of commodity-related derivative MTM losses or gains. See Note 7 – Derivative Financial Instruments for additional information.

(e)

The Ameren Missouri balance relates to the MEEIA. Beginning in January 2014, the MEEIA rider allowed Ameren Missouri to collect from or refund to customers any annual difference in the actual amounts incurred and the amounts collected from customers for the MEEIA program costs and its net shared benefits. Under the MEEIA rider, collections from or refunds to customers occur one year after the program costs and lost revenues are incurred. The Ameren Illinois balance relates to a regulatory tracking mechanism to recover its electric and natural gas costs associated with developing, implementing, and evaluating customer energy efficiency and demand response programs. Any under-recovery or over-recovery will be collected from or refunded to customers over the 12 months following the plan year.


(f)	The difference between Ameren Illinois' annual revenue requirement calculated under the IEIMA's performance-based formula ratemaking framework and the revenue requirement included in customer rates for that year. Subject to ICC approval, these amounts will be collected from or refunded to customers with interest within two years.


(g)	Ameren Illinois' and ATXI's annual revenue requirement reconciliation adjustments calculated pursuant to the FERC's electric transmission formula ratemaking framework. The under-recovery or over-recovery will be recovered from or refunded to customers within two years.


(h)	These costs are being amortized in proportion to the recognition of prior service costs (credits) and actuarial losses (gains) attributable to Ameren’s pension plan and postretirement benefit plans. See Note 11 – Retirement Benefits for additional information.


(i)	Tax benefits related to the equity component of allowance for funds used during construction, as well as the effects of tax rate changes. This will be recovered over the expected life of the related assets.


(j)	Recoverable or refundable removal costs for AROs, including net realized and unrealized gains and losses related to the nuclear decommissioning trust fund investments. See Note 1 – Summary of Significant Accounting Policies – Asset Retirement Obligations and Investments.


(k)	Ameren Missouri’s Callaway energy center operations and maintenance expenses, property taxes, and carrying costs incurred between the plant in-service date and the date the plant was reflected in rates. These costs are being amortized over the remaining life of the energy center's original operating license through 2024.


(l)	Losses related to reacquired debt. These amounts are being amortized over the lives of the related new debt issuances or the original lives of the old debt issuances if no new debt was issued.


(m)	The recoverable portion of accrued environmental site liabilities that will be collected from electric and natural gas customers through ICC-approved cost recovery riders. The period of recovery will depend on the timing of remediation expenditures. See Note 15 – Commitments and Contingencies for additional information.


(n)	Storm costs from 2013 and 2015 deferred in accordance with the IEIMA. These costs are being amortized over five-year periods beginning in 2013 and 2015, respectively.

(o)

Demand-side costs incurred prior to implementation of the MEEIA in 2013, including the costs of developing, implementing, and evaluating customer energy efficiency and demand response programs. Costs incurred from May 2008 through September 2008 are being amortized over a 10-year period that began in March 2009. Costs incurred from October 2008 through December 2009 are being amortized until May 2017. Costs incurred from January 2010 through February 2011 are being amortized over a six-year period that began in August 2011. Costs incurred from March 2011 through July 2012 are being amortized over a six-year period that began in January 2013. Costs incurred from August 2012 through December 2012 are being amortized over a six-year period that began in June 2015.


(p)	The period of recovery will depend on the timing of actual expenditures.


(q)	Ameren Missouri’s costs incurred to enter into and maintain the Missouri Credit Agreement. Additional costs were incurred in December 2014 to amend and restate the Missouri Credit Agreement. These costs are being amortized over the life of the credit facility, ending in December 2019, to construction work in progress, which will be depreciated when assets are placed into service.


(r)	The MoPSC’s May 2010 electric rate order allowed Ameren Missouri to record an allowance for funds used during construction for pollution control equipment at its Sioux energy center until the cost of that equipment was included in customer rates beginning in 2011. These costs are being amortized over the expected life of the Sioux energy center, which is currently through 2033.


(s)	Costs associated with Ameren Missouri's solar rebate program beginning in August 2012 to fulfill its renewable energy portfolio requirement. These costs are being amortized over three years, beginning in June 2015.


(t)	Estimated refunds to transmission customers related to FERC orders. See Ameren Illinois Electric Transmission Rate Refund and FERC Complaint Cases above.


(u)	Unamortized portion of investment tax credits and reductions to deferred tax liabilities recorded at rates in excess of current statutory rates. The unamortized portion of investment tax credits and the reduction to deferred tax liabilities are being amortized over the expected life of the underlying assets.


(v)	The tracker is amortized over three years, beginning from the date the amounts are included in rates. See Note 13 – Income Taxes for additional information.


(w)	Estimated funds collected for the eventual dismantling and removal of plant from service, net of salvage value, upon retirement related to our rate-regulated operations.

(x)

A regulatory tracking mechanism for the difference between the level of bad debt incurred by Ameren Illinois under GAAP and the level of such costs included in electric and natural gas rates. The over-recovery relating to 2013 was refunded to customers from June 2014 through May 2015. The over-recovery relating to 2014 will be refunded to customers from June 2015 through May 2016. The over-recovery relating to 2015 will be refunded to customers from June 2016 through May 2017.

(y)

A regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates. For periods prior to December 2014, the MoPSC's April 2015 electric rate order directed the amortization to occur over three to five years, beginning in June 2015. For periods after December 2014, the amortization period will be determined in a future electric rate case.

(z)

The Ameren Missouri balance includes the costs of renewable energy credits to fulfill Ameren Missouri's renewable energy portfolio requirement from August 2012 through December 2013, which were less than the amount included in rates. These costs are being amortized over three years beginning in June 2015. The Ameren Illinois balance includes funds collected from customers for the purchase of renewable energy credits through IPA procurements for distributed generation. The balance will be amortized as renewable energy credits are purchased.

(aa)

A regulatory tracking mechanism at Ameren Missouri for the difference between the level of storm costs incurred in a particular year and the level of such costs included in rates. For periods prior to December 2014, the MoPSC's April 2015 electric rate order directed the amortization to occur over five years, beginning in June 2015. For periods after December 2014, the amortization period will be determined in a future electric rate case. The April 2015 MoPSC order did not approve the continued use of the regulatory tracking mechanisms for storm costs.