Summary Of Significant Accounting Policies (Regulatory Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 898.1	$ 916.1
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	412.8	408.7
IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	313.0	355.8
Energy conservation cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	62.1	55.1
IPL's electric transmission assets sale [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	27.1	32.5
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	25.0	17.7
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	58.1	46.3
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	672.4	701.4
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	273.1	268.0
IPL [Member] | IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	313.0	355.8
IPL [Member] | Energy conservation cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	16.7	10.0
IPL [Member] | IPL's electric transmission assets sale [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	27.1	32.5
IPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	7.4	5.2
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	35.1	29.9
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	225.7	214.7
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	139.7	140.7
WPL [Member] | IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
WPL [Member] | Energy conservation cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	45.4	45.1
WPL [Member] | IPL's electric transmission assets sale [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
WPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	17.6	12.5
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 23.0	$ 16.4