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Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2025

Fair Value Disclosures [Abstract]

Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis

The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of September 30, 2025, and December 31, 2024:

						September 30, 2025																		December 31, 2024
						Level 1			Level 2			Level 3			Total									Level 1			Level 2			Level 3			Total
Assets:
Ameren Missouri
			Derivative assets – commodity contracts:
			Natural gas			$	—		$	2		$	—		$	2								$	—		$	4		$	—		$	4
			Power			—			—			22			22									—			—			6			6
			Total derivative assets – commodity contracts			$	—		$	2		$	22		$	24								$	—		$	4		$	6		$	10
			Nuclear decommissioning trust fund:
			Equity securities:
			U.S. large capitalization			$	1,001		$	—		$	—		$	1,001								$	911		$	—		$	—		$	911
			Debt securities:
			U.S. Treasury and agency securities			—			235			—			235									—			191			—			191
			Corporate bonds			—			174			—			174									—			145			—			145
			Other			—			84			—			84									—			86			—			86
			Total nuclear decommissioning trust fund			$	1,001		$	493		$	—		$	1,494		(a)						$	911		$	422		$	—		$	1,333		(a)
			Total Ameren Missouri			$	1,001		$	495		$	22		$	1,518								$	911		$	426		$	6		$	1,343
Ameren Illinois
			Derivative assets – commodity contracts:
			Natural gas			$	—		$	4		$	4		$	8								$	—		$	3		$	3		$	6
			Total Ameren Illinois			$	—		$	4		$	4		$	8								$	—		$	3		$	3		$	6
Ameren
			Derivative assets – commodity contracts(b)			$	—		$	6		$	26		$	32								$	—		$	7		$	9		$	16
			Nuclear decommissioning trust fund(c)			1,001			493			—			1,494			(a)						911			422			—			1,333			(a)
			Total Ameren			$	1,001		$	499		$	26		$	1,526								$	911		$	429		$	9		$	1,349
Liabilities:
Ameren Missouri
			Derivative liabilities – commodity contracts:
			Fuel oils			$	3		$	—		$	—		$	3								$	4		$	—		$	—		$	4
			Natural gas			—			8			—			8									—			11			—			11
			Power			—			—			1			1									—			—			—			—
			Total Ameren Missouri			$	3		$	8		$	1		$	12								$	4		$	11		$	—		$	15
Ameren Illinois
			Derivative liabilities – commodity contracts:
			Natural gas			$	1		$	22		$	3		$	26								$	1		$	28		$	6		$	35
			Power			—			—			62			62									—			—			53			53
			Total Ameren Illinois			$	1		$	22		$	65		$	88								$	1		$	28		$	59		$	88
Ameren
			Derivative liabilities – commodity contracts(b)			$	4		$	30		$	66		$	100								$	5		$	39		$	59		$	103

(a)Balance excludes $8 million and $9 million of cash and cash equivalents, receivables, payables, and accrued income, net, for September 30, 2025, and December 31, 2024, respectively.

(b)See the Ameren Missouri and Ameren Illinois sections of the table for a breakout of the fair value of Ameren’s derivative assets and liabilities by type of commodity.

(c)See the Ameren Missouri section of the table for a breakout of the fair value of Ameren’s nuclear decommissioning trust fund by investment type.

Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level Three In The Fair Value Hierarchy

The following table presents the fair value reconciliation of Level 3 power derivative contract assets and liabilities measured at fair value on a recurring basis for the three and nine months ended September 30, 2025 and 2024:

			2025															2024
			Ameren Missouri			Ameren Illinois									Ameren									Ameren Missouri			Ameren Illinois			Ameren
For the three months ended September 30:
Beginning balance at July 1			$	13		$	(76)								$	(63)								$	14		$	(61)		$	(47)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities			12			12									24									(1)			(21)			(22)
Settlements			(4)			2									(2)									(3)			4			1
Ending balance at September 30			$	21		$	(62)								$	(41)								$	10		$	(78)		$	(68)
Change in unrealized gains/(losses) related to assets/liabilities held at September 30			$	11		$	11								$	22								$	(1)		$	(19)		$	(20)
For the nine months ended September 30:
Beginning balance at January 1			$	6		$	(53)								$	(47)								$	4		$	(68)		$	(64)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities			28			(18)									10									13			(23)			(10)
Settlements			(13)			9									(4)									(7)			13			6
Ending balance at September 30			$	21		$	(62)								$	(41)								$	10		$	(78)		$	(68)
Change in unrealized gains/(losses) related to assets/liabilities held at September 30			$	21		$	(17)								$	4								$	10		$	(18)		$	(8)

Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques

The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of September 30, 2025, and December 31, 2024:

									Fair Value																		Weighted Average(b)
			Commodity						Assets						Liabilities			Valuation Technique(s)			Unobservable Input(a)			Range
2025			Power(c)			$			22			$			(63)			Discounted cash flow			Average forward peak and off-peak pricing – forwards/swaps ($/MWh)			33 – 67			43
																					Nodal basis ($/MWh)			(10) – 2			(5)
2024			Power(c)			$			6			$			(53)			Discounted cash flow			Average forward peak and off-peak pricing – forwards/swaps ($/MWh)			32 – 69			45
																					Nodal basis ($/MWh)			(8) – (2)			(5)

(a)Generally, significant increases (decreases) in these inputs in isolation would result in a significantly higher (lower) fair value measurement.

(b)Unobservable inputs were weighted by relative fair value.

(c)Valuations use visible forward prices adjusted for nodal-to-hub basis differentials.

Schedule of Financial Assets and Liabilities

The following table sets forth the carrying amount and, by level within the fair value hierarchy, the fair value of long-term debt (including current portion) disclosed, but not recorded, at fair value as of September 30, 2025, and December 31, 2024:

Long-Term Debt (Including Current Portion):			Carrying Amount(a)												Fair Value
															Level 2						Level 3						Total
			September 30, 2025
Ameren(b)			$	19,201											$	17,532					$	556		(c)			$	18,088
Ameren Missouri(d)			8,246												7,662						—						7,662
Ameren Illinois(d)			6,258												5,815						—						5,815
			December 31, 2024
Ameren(b)			$	17,579											$	15,395					$	538		(c)			$	15,933
Ameren Missouri(d)			7,745												6,926						—						6,926
Ameren Illinois(d)			5,852												5,243						—						5,243

(a)Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $139 million, $63 million, and $56 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of September 30, 2025. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $129 million, $62 million, and $51 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2024.

(b)Amount excludes Ameren (parent)’s repurchase of Ameren Missouri’s senior secured notes and first mortgage bonds and Ameren Illinois’ first mortgage bonds.

(c)The Level 3 fair value amount consists of ATXI’s senior unsecured notes.

(d)Amount includes Ameren Missouri’s senior secured notes and first mortgage bonds and Ameren Illinois’ first mortgage bonds that were repurchased by Ameren (parent).

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