Fair Value Measurements (Fair Value Of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Assets:
Derivative assets	$ 23.5	$ 19.3
Capitalization and liabilities:
Long-term debt (including current maturities)	3,348.4	3,149.9
Long-term debt (including current maturities)	3,712.3	3,860.5
Cumulative preferred stock		212.6
Cumulative preferred stock	200.0	145.1
Cumulative preferred stock	167.0
Cumulative preferred stock	0	60.0
Derivative liabilities	17.6	33.5
IPL [Member]
Assets:
Derivative assets	19.5	14.5
Capitalization and liabilities:
Long-term debt (including current maturities)	1,563.4	1,363.4
Long-term debt (including current maturities)	1,726.4	1,679.9
Cumulative preferred stock	200.0	145.1
Cumulative preferred stock	167.0	151.8
Derivative liabilities	3.6	13.1
WPL [Member]
Assets:
Derivative assets	4.0	4.8
Capitalization and liabilities:
Long-term debt (including current maturities)	1,339.1	1,339.1
Long-term debt (including current maturities)	1,532.9	1,713.3
Cumulative preferred stock	0	60.8
Cumulative preferred stock	0	60.0
Derivative liabilities	14.0	20.4
Carrying Amount [Member]
Assets:
Derivative assets	26.7	26.2
Deferred proceeds (sales of receivables)	203.5	66.8
Capitalization and liabilities:
Long-term debt (including current maturities)	3,336.3	3,138.1
Cumulative preferred stock		205.1
Cumulative preferred stock	200.0
Derivative liabilities	20.8	40.4
Carrying Amount [Member] | IPL [Member]
Assets:
Derivative assets	21.1	17.5
Deferred proceeds (sales of receivables)	203.5	66.8
Capitalization and liabilities:
Long-term debt (including current maturities)	1,558.4	1,359.5
Cumulative preferred stock	200.0	145.1
Derivative liabilities	5.2	16.1
Carrying Amount [Member] | WPL [Member]
Assets:
Derivative assets	5.6	8.7
Deferred proceeds (sales of receivables)	0	0
Capitalization and liabilities:
Long-term debt (including current maturities)	1,332.1	1,331.5
Cumulative preferred stock	0	60.0
Derivative liabilities	15.6	24.3
Fair Value [Member]
Assets:
Derivative assets	26.7	26.2
Deferred proceeds (sales of receivables)	203.5	66.8
Capitalization and liabilities:
Long-term debt (including current maturities)	3,712.3	3,860.5
Cumulative preferred stock		212.6
Cumulative preferred stock	167.0
Derivative liabilities	20.8	40.4
Fair Value [Member] | IPL [Member]
Assets:
Derivative assets	21.1	17.5
Deferred proceeds (sales of receivables)	203.5	66.8
Capitalization and liabilities:
Long-term debt (including current maturities)	1,726.4	1,679.9
Cumulative preferred stock	167.0	151.8
Derivative liabilities	5.2	16.1
Fair Value [Member] | WPL [Member]
Assets:
Derivative assets	5.6	8.7
Deferred proceeds (sales of receivables)	0	0
Capitalization and liabilities:
Long-term debt (including current maturities)	1,532.9	1,713.3
Cumulative preferred stock	0	60.8
Derivative liabilities	$ 15.6	$ 24.3