Benefit Plans [Line Items]

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- Definition

Carrying value of entity deferred compensation obligations interest and equity accounts

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- Definition

Common stock percentage in assets held saving plans.

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- Definition

Deferred Compensation Plan, Base Salary And Incentive Compensation, Percentage

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- Definition

Defined Benefit Pension And Other Postretirement Benefits Plans, Total Plan Assets Percentage, On Common Stock

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- Definition

Defined Benefit Plan, Plan Asset Threshold for Long-term Allocation Targets

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Instrument Valuation Based On Shares of Common Stock, Number of Shares

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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

Price of a single share of a number of saleable stocks of a company.

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- Definition

Percentage of vesting of award under share-based payment arrangement.

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- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

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Benefit Plans (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Benefit Plans [Line Items]
Total plan assets (less than 1%), percentage of common stock	1.00%	1.00%
Common stock percentage in assets held in 401(k) saving plans	11.50%	11.50%
Unrecognized compensation cost	$ 5.4
Alliant Energy common stock closing price on December 31, 2019 (in dollars per share)	$ 54.72
Percentage of base salary and short-term cash incentive compensation	100.00%
Carrying value of deferred compensation obligations	$ 21.2	$ 21.0
Performance Shares Equity Awards [Member]
Benefit Plans [Line Items]
Performance period	3 years
Performance Shares and Performance Units Liability Awards [Member]
Benefit Plans [Line Items]
Performance period	3 years
Instrument valuation based on shares of common stock, number of shares	1
Restricted Stock Units Equity Awards [Member]
Benefit Plans [Line Items]
Performance period	3 years
Instrument valuation based on shares of common stock, number of shares	1
Restricted Stock Units Liability Awards [Member]
Benefit Plans [Line Items]
Performance period	3 years
Instrument valuation based on shares of common stock, number of shares	1
Performance Restricted Stock Units Equity Awards [Member]
Benefit Plans [Line Items]
Performance period	3 years
Instrument valuation based on shares of common stock, number of shares	1
Minimum [Member]
Benefit Plans [Line Items]
Unrecognized compensation cost recognized over a weighted average period	1 year
Minimum [Member] \| Performance Shares Equity Awards [Member]
Benefit Plans [Line Items]
Actual number of shares paid out upon vesting, percentage of target shares	0.00%
Minimum [Member] \| Performance Shares and Performance Units Liability Awards [Member]
Benefit Plans [Line Items]
Actual number of shares paid out upon vesting, percentage of target shares	0.00%
Minimum [Member] \| Performance Restricted Stock Units Equity Awards [Member]
Benefit Plans [Line Items]
Actual number of shares paid out upon vesting, percentage of target shares	0.00%
Maximum [Member]
Benefit Plans [Line Items]
Unrecognized compensation cost recognized over a weighted average period	2 years
Maximum [Member] \| Performance Shares Equity Awards [Member]
Benefit Plans [Line Items]
Actual number of shares paid out upon vesting, percentage of target shares	200.00%
Maximum [Member] \| Performance Shares and Performance Units Liability Awards [Member]
Benefit Plans [Line Items]
Actual number of shares paid out upon vesting, percentage of target shares	200.00%
Maximum [Member] \| Performance Restricted Stock Units Equity Awards [Member]
Benefit Plans [Line Items]
Actual number of shares paid out upon vesting, percentage of target shares	200.00%
IPL [Member]
Benefit Plans [Line Items]
Unrecognized compensation cost	$ 3.0
WPL [Member]
Benefit Plans [Line Items]
Unrecognized compensation cost	2.2
Other Postretirement Benefits Plans [Member]
Benefit Plans [Line Items]
Plan asset threshold for long-term allocation targets	5.0
Other Postretirement Benefits Plans [Member] \| IPL [Member]
Benefit Plans [Line Items]
Plan asset threshold for long-term allocation targets	5.0
Other Postretirement Benefits Plans [Member] \| WPL [Member]
Benefit Plans [Line Items]
Plan asset threshold for long-term allocation targets	$ 5.0
Omnibus Incentive Plan [Member]
Benefit Plans [Line Items]
Shares available for issuance under the Amended and Restated OIP	6,400,000
Shares included in diluted earnings per share (in shares)	343,396