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Regulatory Matters Regulatory Matters (Revenue Requirement Adjustment) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenue Requirement Adjustment [Line Items]
Increase to electric revenues	$ 771.2	$ 798.1	$ 2,090.9	$ 2,043.4
Alliant Energy and IPL [Member] | Revenue Requirement Adjustment [Member]
Revenue Requirement Adjustment [Line Items]
Increase to electric revenues	$ 4.0	$ 7.0	$ 11.0	$ 18.0

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- Definition

Revenue derived from the regulated (by a federal, state, or local government or agency) generation, transmission and distribution of electricity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1(b))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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