Retirement Benefits (Tables)

12 Months Ended

Dec. 31, 2016

Summary Of Benefit Liability Recorded

The following table presents the net benefit liability recorded on the balance sheets of each of the Ameren Companies as of December 31, 2016 and 2015:

	2016		2015
Ameren(a)	$	774	$	567
Ameren Missouri	293		236
Ameren Illinois	315		219

(a) Includes amounts for Ameren registrant and nonregistrant subsidiaries.

Funded Status Of Benefit Plans And Amounts Included In Regulatory Assets And OCI

The following table presents the funded status of Ameren's pension and postretirement benefit plans as of December 31, 2016 and 2015. It also provides the amounts included in regulatory assets and accumulated OCI at December 31, 2016 and 2015, that have not been recognized in net periodic benefit costs.

	2016						2015
	Pension Benefits(a)				Postretirement Benefits(a)		Pension Benefits(a)				Postretirement Benefits(a)
Accumulated benefit obligation at end of year	$	4,288		$	(b)		$	3,995		$	(b)
Change in benefit obligation:
Net benefit obligation at beginning of year	$	4,197		$	1,094		$	4,410		$	1,203
Service cost	81				19		92				24
Interest cost	185				50		174				48
Participant contributions	—				8		—				8
Actuarial (gain) loss	265				52		(256		)		(133	)
Settlement	—				—		(2		)		—
Benefits paid	(210		)		(54	)	(221		)		(56	)
Federal subsidy on benefits paid	(b)				1		(b)				—
Net benefit obligation at end of year	4,518				1,170		4,197				1,094
Change in plan assets:
Fair value of plan assets at beginning of year	3,653				1,071		3,794				1,109
Actual return on plan assets	313				73		(29		)		(8	)
Employer contributions	57				2		111				18
Federal subsidy on benefits paid	(b)				1		(b)				—
Participant contributions	—				8		—				8
Settlements	—				—		(2		)		—
Benefits paid	(210		)		(54	)	(221		)		(56	)
Fair value of plan assets at end of year	3,813				1,101		3,653				1,071
Funded status – deficiency	705				69		544				23
Accrued benefit cost at December 31	$	705		$	69		$	544		$	23
Amounts recognized in the balance sheet consist of:
Noncurrent asset(c)	$	—		$	—		$	—		$	(18	)
Current liability(d)	3				2		3				2
Noncurrent liability	702				67		541				39
Net liability recognized	$	705		$	69		$	544		$	23
Amounts recognized in regulatory assets consist of:
Net actuarial (gain) loss	$	535		$	(29	)	$	395		$	(82	)
Prior service cost (credit)	(4		)		(8	)	(5		)		(11	)
Amounts (pretax) recognized in accumulated OCI consist of:
Net actuarial (gain) loss	43				—		17				(3	)
Prior service cost (credit)	—				(1	)	—				—
Total	$	574		$	(38	)	$	407		$	(96	)

(a) Includes amounts for Ameren registrant and nonregistrant subsidiaries.

(b) Not applicable.

(c) Included in "Other assets" on Ameren's consolidated balance sheet.

(d) Included in "Other current liabilities" on Ameren's consolidated balance sheet.

Assumptions Used To Determine Benefit Obligations

The following table presents the assumptions used to determine our benefit obligations at December 31, 2016 and 2015:

	Pension Benefits				Postretirement Benefits
	2016		2015		2016		2015
Discount rate at measurement date	4.00	%	4.50	%	4.00	%	4.50	%
Increase in future compensation	3.50		3.50		3.50		3.50
Medical cost trend rate (initial)	(a)		(a)		5.00		5.00
Medical cost trend rate (ultimate)	(a)		(a)		5.00		5.00

(a) Not applicable

Schedule Of Cash Contributions Made To Benefit Plans

The following table presents the cash contributions made to our defined benefit retirement plan and to our postretirement plans during 2016, 2015, and 2014:

	Pension Benefits						Postretirement Benefits
	2016		2015		2014		2016		2015		2014
Ameren Missouri	$	21	$	47	$	41	$	1	$	8	$	3
Ameren Illinois	30		45		39		1		8		2
Other	6		19		19		—		2		1
Ameren	57		111		99		2		18		6

Target Allocation Of The Plans' Asset Categories

The following table presents our target allocations for 2017 and our pension and postretirement plans’ asset categories as of December 31, 2016 and 2015:

Asset Category	Target Allocation 2017	Percentage of Plan Assets at December  31,
		2016		2015
Pension Plan:
Cash and cash equivalents	0% – 5%	1	%	1	%
Equity securities:
U.S. large-capitalization	29% – 39%	34	%	34	%
U.S. small- and mid-capitalization	3% – 13%	9	%	7	%
International and emerging markets	9% – 19%	14	%	13	%
Total equity	51% – 61%	57	%	54	%
Debt securities	35% – 45%	37	%	40	%
Real estate	0% –  9%	5	%	5	%
Private equity	0% –  5%	(a)		(a)
Total		100	%	100	%
Postretirement Plans:
Cash and cash equivalents	0% – 7%	3	%	4	%
Equity securities:
U.S. large-capitalization	34% – 44%	40	%	39	%
U.S. small- and mid-capitalization	2% – 12%	7	%	7	%
International	9% – 19%	14	%	13	%
Total equity	55% – 65%	61	%	59	%
Debt securities	33% – 43%	36	%	37	%
Total		100	%	100	%

(a) Less than 1% of plan assets.

Components Of Net Periodic Benefit Cost

The following table presents the components of the net periodic benefit cost of Ameren's pension and postretirement benefit plans during 2016, 2015, and 2014:

	Pension Benefits			Postretirement Benefits
2016
Service cost	$	81		$	19
Interest cost	185			50
Expected return on plan assets	(253		)	(72		)
Amortization of:
Prior service credit	(1		)	(5		)
Actuarial (gain) loss	32			(11		)
Net periodic benefit cost (benefit)	$	44		$	(19	)
2015
Service cost	$	92		$	24
Interest cost	174			48
Expected return on plan assets	(248		)	(68		)
Amortization of:
Prior service credit	(1		)	(5		)
Actuarial loss	74			5
Settlement loss	1			—
Net periodic benefit cost (benefit)	$	92		$	4
2014
Service cost	$	79		$	19
Interest cost	183			50
Expected return on plan assets	(229		)	(65		)
Amortization of:
Prior service credit	(1		)	(5		)
Actuarial (gain) loss	49			(7		)
Net periodic benefit cost (benefit)	$	81		$	(8	)

Summary Of Estimated Amortizable Amounts From Regulatory Assets and Accumulated OCI Into Net Periodic Benefit Cost

The estimated amounts that will be amortized from regulatory assets and accumulated OCI into Ameren's net periodic benefit cost in 2017 are as follows:

	Pension Benefits(a)			Postretirement Benefits(a)
Regulatory assets:
Prior service credit	$	(1	)	$	(5	)
Net actuarial (gain) loss	50			(7		)
Accumulated OCI:
Net actuarial loss	4			—
Total	$	53		$	(12	)

(a) Includes amounts for Ameren registrant and nonregistrant subsidiaries.

Summary Of Benefit Plan Costs Incurred

The Ameren Companies are responsible for their share of the pension and postretirement benefit costs. The following table presents the pension costs and the postretirement benefit costs incurred and included in continuing operations for the years ended December 31, 2016, 2015, and 2014:

	Pension Costs							Postretirement Costs
	2016			2015		2014		2016			2015			2014
Ameren Missouri(a)	$	26		$	54	$	50	$	(5	)	$	8		$	3
Ameren Illinois	22			38		30		(13		)	(3		)	(9		)
Other	(4		)	—		1		(1		)	(1		)	(2		)
Ameren	44			92		81		(19		)	4			(8		)

(a) Does not include the impact of the 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.

Schedule Of Expected Payments From Qualified Trust And Company Funds

The expected pension and postretirement benefit payments from qualified trust and company funds, which reflect expected future service, as of December 31, 2016, are as follows:

	Pension Benefits				Postretirement Benefits
	Paid from Qualified Trust Funds		Paid from          Company       Funds		Paid from          Qualified       Trust Funds		Paid from          Company       Funds
2017	$	248	$	3	$	54	$	2
2018	254		3		57		2
2019	261		3		59		2
2020	265		3		61		2
2021	273		3		63		2
2022 – 2026	1,405		13		331		12

Assumptions Used To Determine Net Periodic Benefit Cost

The following table presents the assumptions used to determine net periodic benefit cost for our pension and postretirement benefit plans for the years ended December 31, 2016, 2015, and 2014:

	Pension Benefits						Postretirement Benefits
	2016		2015		2014		2016		2015		2014
Discount rate at measurement date	4.50	%	4.00	%	4.75	%	4.50	%	4.00	%	4.75	%
Expected return on plan assets	7.00		7.25		7.25		7.00		7.00		7.00
Increase in future compensation	3.50		3.50		3.50		3.50		3.50		3.50
Medical cost trend rate (initial)	(a)		(a)		(a)		5.00		5.00		5.00
Medical cost trend rate (ultimate)	(a)		(a)		(a)		5.00		5.00		5.00

(a) Not applicable

Schedule Of Potential Changes In Key Assumptions

The table below reflects the sensitivity of Ameren’s plans to potential changes in key assumptions:

	Pension Benefits					Postretirement Benefits
	Service Cost and Interest Cost			Projected     Benefit      Obligation		Service Cost     and Interest     Cost			Postretirement       Benefit        Obligation
0.25% decrease in discount rate	$	(1	)	$	142	$	—		$	38
0.25% increase in salary scale	2			16		—			—
1.00% increase in annual medical trend	—			—		3			54
1.00% decrease in annual medical trend	—			—		(3		)	(54		)

Schedule Of Matching Contributions

The following table presents the portion of the matching contribution to the Ameren 401(k) plan attributable to the continuing operations for each of the Ameren Companies for the years ended December 31, 2016, 2015, and 2014:

	2016		2015		2014
Ameren Missouri	$	16	$	16	$	16
Ameren Illinois	12		12		11
Other	1		1		1
Ameren	29		29		28

Pension Benefits

Target Allocation Of The Plans' Asset Categories

The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plan assets measured at fair value as of December 31, 2016:

	Quoted Prices in Active Markets for Identified Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Other Unobservable Inputs (Level 3)		Measured at NAV(a)		Total
Cash and cash equivalents	$	—	$	—	$	—	$	33	$	33
Equity securities:
U.S. large-capitalization	—		—		—		1,352		1,352
U.S. small- and mid-capitalization	361		—		—		—		361
International and emerging markets	133		—		—		389		522
Debt securities:
Corporate bonds	—		617		—		13		630
Municipal bonds	—		95		—		—		95
U.S. Treasury and agency securities	—		701		—		—		701
Other	—		21		—		—		21
Real estate	—		—		—		202		202
Private equity	—		—		—		6		6
Total	$	494	$	1,434	$	—	$	1,995	$	3,923
Less: Medical benefit assets at December 31(b)									(132		)
Plus: Net receivables at December 31(c)									22
Fair value of pension plans assets at year end									$	3,813

(a) Reflects the adoption of the new authoritative accounting guidance related to investments measured at the NAV practical expedient. See Note 1 - Summary of Significant Accounting Policies for additional information.

(b) Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation.

(c) Receivables related to pending security sales, offset by payables related to pending security purchases.

The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plan assets measured at fair value as of December 31, 2015:

	Quoted Prices in Active Markets for Identified Assets or Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Other Unobservable Inputs (Level 3)		Measured at NAV(a)		Total
Cash and cash equivalents	$	—	$	—	$	—	$	20	$	20
Equity securities:
U.S. large-capitalization	—		—		—		1,296		1,296
U.S. small- and mid-capitalization	268		—		—		—		268
International and emerging markets	122		126		—		243		491
Debt securities:
Corporate bonds	—		617		—		14		631
Municipal bonds	—		104		—		—		104
U.S. Treasury and agency securities	6		751		—		—		757
Other	—		5		—		—		5
Real estate	—		—		—		168		168
Private equity	—		—		—		8		8
Total	$	396	$	1,603	$	—	$	1,749	$	3,748
Less: Medical benefit assets at December 31(b)									(123		)
Plus: Net receivables at December 31(c)									28
Fair value of pension plans assets at year end									$	3,653

(a) Reflects the adoption of the new authoritative accounting guidance related to investments measured at the NAV practical expedient. See Note 1 - Summary of Significant Accounting Policies for additional information.

(b) Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation.

(c) Receivables related to pending security sales, offset by payables related to pending security purchases.

Postretirement Benefits

Target Allocation Of The Plans' Asset Categories

The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans assets measured at fair value as of December 31, 2016:

	Quoted Prices in Active Markets for Identified Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Other Unobservable Inputs (Level 3)		Measured at NAV(a)		Total
Cash and cash equivalents	$	53	$	—	$	—	$	—	$	53
Equity securities:
U.S. large-capitalization	291		—		—		101		392
U.S. small- and mid-capitalization	72		—		—		—		72
International	40		—		—		92		132
Other	—		7		—		—		7
Debt securities:
Corporate bonds	—		141		—		—		141
Municipal bonds	—		110		—		—		110
U.S. Treasury and agency securities	—		68		—		—		68
Other	—		—		—		19		19
Total	$	456	$	326	$	—	$	212	$	994
Plus: Medical benefit assets at December 31(b)									132
Less: Net payables at December 31(c)									(25		)
Fair value of postretirement benefit plans assets at year end									$	1,101

(a) Reflects the adoption of the new authoritative accounting guidance related to investments measured at the NAV practical expedient. See Note 1 - Summary of Significant Accounting Policies for additional information.

(b) Medical benefit (health and welfare) component for 401(h) accounts to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above.

(c) Payables related to pending security purchases, offset by interest receivables and receivables related to pending security sales.

The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans assets measured at fair value as of December 31, 2015:

	Quoted Prices in Active Markets for Identified Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Other Unobservable Inputs (Level 3)		Measured at NAV(a)		Total
Cash and cash equivalents	$	61	$	—	$	—	$	—	$	61
Equity securities:
U.S. large-capitalization	272		—		—		98		370
U.S. small- and mid-capitalization	65		—		—		—		65
International	33		38		—		55		126
Other	—		7		—		—		7
Debt securities:
Corporate bonds	—		138		—		—		138
Municipal bonds	—		114		—		—		114
U.S. Treasury and agency securities	—		55		—		—		55
Other	—		4		—		36		40
Total	$	431	$	356	$	—	$	189	$	976
Plus: Medical benefit assets at December 31(a)									123
Less: Net payables at December 31(b)									(28		)
Fair value of postretirement benefit plans assets at year end									$	1,071

(a) Reflects the adoption of the new authoritative accounting guidance related to investments measured at the NAV practical expedient. See Note 1 - Summary of Significant Accounting Policies for additional information.

(b) Medical benefit (health and welfare) component for 401(h) accounts to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above.

(c) Payables related to pending security purchases, offset by Medicare, interest receivables, and receivables related to pending security sales.