Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets, gross	$ (677.1)	$ (768.5)
Deferred tax liabilities, gross	3,058.3	2,939.5
Deferred tax (assets) and liabilities, net	2,381.2	2,171.0
Current deferred tax assets	0.0	(150.1)
Non-current deferred tax liabilities	2,381.2	2,321.1
Deferred tax liabilities, net of deferred tax assets	2,381.2	2,171.0
IPL [Member]
Deferred tax assets, gross	(297.6)	(362.3)
Deferred tax liabilities, gross	1,675.6	1,628.6
Deferred tax (assets) and liabilities, net	1,378.0	1,266.3
Current deferred tax assets	0.0	(104.0)
Non-current deferred tax liabilities	1,378.0	1,370.3
Deferred tax liabilities, net of deferred tax assets	1,378.0	1,266.3
WPL [Member]
Deferred tax assets, gross	(228.4)	(245.4)
Deferred tax liabilities, gross	1,233.8	1,174.8
Deferred tax (assets) and liabilities, net	1,005.4	929.4
Current deferred tax assets	0.0	(37.7)
Non-current deferred tax liabilities	1,005.4	967.1
Deferred tax liabilities, net of deferred tax assets	1,005.4	929.4
Property [Member]
Deferred tax assets, gross	0.0	0.0
Deferred tax liabilities, gross	2,762.9	2,627.8
Deferred tax (assets) and liabilities, net	2,762.9	2,627.8
Property [Member] | IPL [Member]
Deferred tax assets, gross	0.0	0.0
Deferred tax liabilities, gross	1,587.8	1,545.1
Deferred tax (assets) and liabilities, net	1,587.8	1,545.1
Property [Member] | WPL [Member]
Deferred tax assets, gross	0.0	0.0
Deferred tax liabilities, gross	1,027.0	963.0
Deferred tax (assets) and liabilities, net	1,027.0	963.0
Investment In ATC [Member]
Deferred tax assets, gross	0.0	0.0
Deferred tax liabilities, gross	138.1	131.6
Deferred tax (assets) and liabilities, net	138.1	131.6
Investment In ATC [Member] | WPL [Member]
Deferred tax assets, gross	0.0	0.0
Deferred tax liabilities, gross	138.9	132.1
Deferred tax (assets) and liabilities, net	138.9	132.1
Net operating losses carryforward - state [Member]
Deferred tax assets, gross	(38.3)	(45.7)
Deferred tax liabilities, gross	0.0	0.0
Deferred tax (assets) and liabilities, net	(38.3)	(45.7)
Regulatory liability - IPL's tax benefit riders [Member]
Deferred tax assets, gross	(66.1)	(100.9)
Deferred tax liabilities, gross	0.0	0.0
Deferred tax (assets) and liabilities, net	(66.1)	(100.9)
Regulatory liability - IPL's tax benefit riders [Member] | IPL [Member]
Deferred tax assets, gross	(66.1)	(100.9)
Deferred tax liabilities, gross	0.0	0.0
Deferred tax (assets) and liabilities, net	(66.1)	(100.9)
Federal credit carryforwards [Member]
Deferred tax assets, gross	(236.4)	(201.0)
Deferred tax liabilities, gross	0.0	0.0
Deferred tax (assets) and liabilities, net	(236.4)	(201.0)
Federal credit carryforwards [Member] | IPL [Member]
Deferred tax assets, gross	(81.7)	(66.5)
Deferred tax liabilities, gross	0.0	0.0
Deferred tax (assets) and liabilities, net	(81.7)	(66.5)
Federal credit carryforwards [Member] | WPL [Member]
Deferred tax assets, gross	(95.5)	(76.7)
Deferred tax liabilities, gross	0.0	0.0
Deferred tax (assets) and liabilities, net	(95.5)	(76.7)
Net operating losses carryforwards - federal [Member]
Deferred tax assets, gross	(250.9)	(332.8)
Deferred tax liabilities, gross	0.0	0.0
Deferred tax (assets) and liabilities, net	(250.9)	(332.8)
Net operating losses carryforwards - federal [Member] | IPL [Member]
Deferred tax assets, gross	(113.1)	(157.8)
Deferred tax liabilities, gross	0.0	0.0
Deferred tax (assets) and liabilities, net	(113.1)	(157.8)
Net operating losses carryforwards - federal [Member] | WPL [Member]
Deferred tax assets, gross	(105.1)	(131.6)
Deferred tax liabilities, gross	0.0	0.0
Deferred tax (assets) and liabilities, net	(105.1)	(131.6)
Other [Member]
Deferred tax assets, gross	(85.4)	(88.1)
Deferred tax liabilities, gross	157.3	180.1
Deferred tax (assets) and liabilities, net	71.9	92.0
Other [Member] | IPL [Member]
Deferred tax assets, gross	(36.7)	(37.1)
Deferred tax liabilities, gross	87.8	83.5
Deferred tax (assets) and liabilities, net	51.1	46.4
Other [Member] | WPL [Member]
Deferred tax assets, gross	(27.8)	(37.1)
Deferred tax liabilities, gross	67.9	79.7
Deferred tax (assets) and liabilities, net	$ 40.1	$ 42.6