Benefit Plans (Medical Cost Trend On Covered Charges) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012
Effect on total of service and interest cost components, 1% Increase	$ 0.4
Effect on total of service and interest cost components, 1% Decrease	(0.4)
Effect on postretirement benefit obligation, 1% Increase	2.6
Effect on postretirement benefit obligation, 1% Decrease	(2.4)
IPL [Member]
Effect on total of service and interest cost components, 1% Increase	0.2
Effect on total of service and interest cost components, 1% Decrease	(0.2)
Effect on postretirement benefit obligation, 1% Increase	1.2
Effect on postretirement benefit obligation, 1% Decrease	(1.1)
WPL [Member]
Effect on total of service and interest cost components, 1% Increase	0.2
Effect on total of service and interest cost components, 1% Decrease	(0.2)
Effect on postretirement benefit obligation, 1% Increase	1.2
Effect on postretirement benefit obligation, 1% Decrease	$ (1.2)

Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

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- Definition

Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

+ References

+ Details

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- Definition

The effect of a one-percentage-point increase in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (m)

-URI http://asc.fasb.org/extlink&oid=21915506&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph m

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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- Definition

The effect of a one-percentage-point increase in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
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