Fair Value Measurements (Fair Value Of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Assets:
Derivative assets	$ 119.0	$ 26.7
Deferred proceeds (sales of receivables)	193.7	203.5
Capitalization and liabilities:
Long-term debt (including current maturities)	3,907.4	3,712.3
Cumulative preferred stock	200.0	200.0
Cumulative preferred stock	199.2	167.0
Derivative liabilities	13.3	20.8
IPL [Member]
Assets:
Derivative assets	73.0	21.1
Deferred proceeds (sales of receivables)	193.7	203.5
Capitalization and liabilities:
Long-term debt (including current maturities)	1,821.3	1,726.4
Cumulative preferred stock	200.0	200.0
Cumulative preferred stock	199.2	167.0
Derivative liabilities	6.3	5.2
WPL [Member]
Assets:
Derivative assets	46.0	5.6
Capitalization and liabilities:
Long-term debt (including current maturities)	1,627.1	1,532.9
Derivative liabilities	7.0	15.6
Carrying Amount [Member]
Assets:
Derivative assets	119.0	26.7
Deferred proceeds (sales of receivables)	193.7	203.5
Capitalization and liabilities:
Long-term debt (including current maturities)	3,338.9	3,336.3
Cumulative preferred stock	200.0	200.0
Derivative liabilities	13.3	20.8
Carrying Amount [Member] \| IPL [Member]
Assets:
Derivative assets	73.0	21.1
Deferred proceeds (sales of receivables)	193.7	203.5
Capitalization and liabilities:
Long-term debt (including current maturities)	1,558.7	1,558.4
Cumulative preferred stock	200.0	200.0
Derivative liabilities	6.3	5.2
Carrying Amount [Member] \| WPL [Member]
Assets:
Derivative assets	46.0	5.6
Capitalization and liabilities:
Long-term debt (including current maturities)	1,332.3	1,332.1
Derivative liabilities	7.0	15.6
Fair Value [Member]
Assets:
Derivative assets	119.0	26.7
Deferred proceeds (sales of receivables)	193.7	203.5
Capitalization and liabilities:
Long-term debt (including current maturities)	3,907.4	3,712.3
Cumulative preferred stock	199.2	167.0
Derivative liabilities	13.3	20.8
Fair Value [Member] \| IPL [Member]
Assets:
Derivative assets	73.0	21.1
Deferred proceeds (sales of receivables)	193.7	203.5
Capitalization and liabilities:
Long-term debt (including current maturities)	1,821.3	1,726.4
Cumulative preferred stock	199.2	167.0
Derivative liabilities	6.3	5.2
Fair Value [Member] \| WPL [Member]
Assets:
Derivative assets	46.0	5.6
Capitalization and liabilities:
Long-term debt (including current maturities)	1,627.1	1,532.9
Derivative liabilities	$ 7.0	$ 15.6

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Fair value of deferred proceeds of receivables sold

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Preferred Stock Fair Value

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Aggregate par or stated value of issued nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable preferred shares, par value and other disclosure concepts are in another section within stockholders' equity.

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