Summary Of Significant Accounting Policies (Regulatory Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 916.1	$ 910.1
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	701.4	721.3
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	214.7	188.8
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	408.7	404.9
Cost of removal obligations [Member] | IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	268.0	261.9
Cost of removal obligations [Member] | WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	140.7	143.0
IPL's tax benefit rider [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	355.8	349.6
IPL's tax benefit rider [Member] | IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	355.8	349.6
IPL's tax benefit rider [Member] | WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Energy conservation cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	55.1	29.6
Energy conservation cost recovery [Member] | IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	10.0	4.7
Energy conservation cost recovery [Member] | WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	45.1	24.9
IPL's electric transmission assets sale [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	32.5	45.1
IPL's electric transmission assets sale [Member] | IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	32.5	45.1
IPL's electric transmission assets sale [Member] | WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	17.7	23.8
Commodity cost recovery [Member] | IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	5.2	23.2
Commodity cost recovery [Member] | WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	12.5	0.6
IPL's DAEC Sale [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	9.5	14.6
IPL's DAEC Sale [Member] | IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	9.5	14.6
IPL's DAEC Sale [Member] | WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	36.8	42.5
Other [Member] | IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	20.4	22.2
Other [Member] | WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 16.4	$ 20.3