[Line Items] for Accounting Policies [Table]

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- Definition

Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement

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The resettlement of MISO-related purchase and sale transactions.

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- Definition

Number of Months Between Callaway Maintenance Outages

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- Definition

Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement

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- Definition

Provision For Depreciation Percent Of Average Depreciable Cost

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- Definition

Public Utilities, Area Serviced

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- Definition

Public Utilities, Number of Customers

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- Definition

Workforce Utilizing Remote Work Arrangement

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- Definition

Carrying amount as of the balance sheet date of amounts which could be received based on the terms of the insurance contract upon surrendering life policies owned by the entity.

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- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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- Definition

Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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- Definition

Amount before allowance of loans made to policy and contract holders using their life insurance contracts' cash value or separate accounts as collateral. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums over and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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- Definition

Portion of equity (net assets) in a variable interest entity (VIE) not attributable, directly or indirectly, to the parent entity. That is, this is the portion of equity in a VIE that is attributable to the noncontrolling interest (previously referred to as minority interest).

+ References

No definition available.

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- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Amount of increase (decrease) of physical assets used in the normal conduct of business and not intended for resale, from reclassification, impairment, donation, or changes classified as other. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Amount of the unrecorded obligation to transfer funds in the future for fixed or minimum amounts or quantities of goods or services at fixed or minimum prices (for example, as in take-or-pay contracts or throughput contracts).

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Summary Of Significant Accounting Policies (Narrative) (Details) customer in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) mi² customer segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2020
Accounting Policies [Line Items]
Workforce Utilizing Remote Work Arrangement	50.00%			65.00%
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	29.00%	18.00%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 133,000,000	$ 75,000,000
Goodwill	$ 411,000,000	411,000,000
Number of reportable segments \| segment	4
Goodwill, Impairment Loss	$ 0
Noncontrolling Interest in Variable Interest Entity	37,000,000	28,000,000
Unrecorded Unconditional Purchase Obligation	1,969,000,000
Cash Surrender Value of Life Insurance	272,000,000	264,000,000
Loans, Gross, Insurance Policy	107,000,000	$ 114,000,000
MISO Resettlements	$ 0
Union Electric Company
Accounting Policies [Line Items]
Public Utilities, Area Serviced \| mi²	24,000
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	22.00%	18.00%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 40,000,000	$ 30,000,000
Number of Months Between Callaway Maintenance Outages	18 months
Unrecorded Unconditional Purchase Obligation	$ 1,390,000,000
Ameren Illinois Company
Accounting Policies [Line Items]
Public Utilities, Area Serviced \| mi²	43,700
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	35.00%	20.00%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 93,000,000	$ 45,000,000
Goodwill	$ 411,000,000	411,000,000
Number of reportable segments \| segment	3
Goodwill, Impairment Loss	$ 0
Unrecorded Unconditional Purchase Obligation	570,000,000
Cash Surrender Value of Life Insurance	$ 115,000,000	$ 123,000,000
Minimum
Accounting Policies [Line Items]
Percent of average depreciable cost	3.00%	3.00%	3.00%
Maximum
Accounting Policies [Line Items]
Percent of average depreciable cost	4.00%	4.00%	4.00%
Electric \| Union Electric Company
Accounting Policies [Line Items]
Public Utilities, Number of Customers \| customer	1.2
Power \| Ameren Illinois Company
Accounting Policies [Line Items]
Public Utilities, Number of Customers \| customer	1.2
Natural gas \| Union Electric Company
Accounting Policies [Line Items]
Public Utilities, Number of Customers \| customer	0.1
Natural gas \| Ameren Illinois Company
Accounting Policies [Line Items]
Public Utilities, Number of Customers \| customer	0.8
Ameren Illinois Electric Distribution
Accounting Policies [Line Items]
Goodwill	$ 238,000,000
Ameren Illinois Gas
Accounting Policies [Line Items]
Goodwill	80,000,000
Ameren Illinois Transmission
Accounting Policies [Line Items]
Goodwill	93,000,000
Ameren Transmission
Accounting Policies [Line Items]
Goodwill	93,000,000
AROs \| Union Electric Company
Accounting Policies [Line Items]
Noncash Depreciation related to ARO	28,000,000	$ 18,000,000	$ 14,000,000
Partnership Funding Commitment [Member]
Accounting Policies [Line Items]
Unrecorded Unconditional Purchase Obligation	$ 35,000,000