Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Deferred tax liabilities, property	$ 2,021.5	$ 1,975.5
Deferred tax liabilities, other	85.1	80.5
Total deferred tax liabilities	2,217.4	2,158.4
Deferred tax assets, federal credit carryforwards	355.4	299.1
Deferred tax assets, net operating losses carryforwards - federal	60.5	158.6
Deferred tax assets, net operating losses carryforwards - state	36.6	47.0
Deferred tax assets, other	60.5	59.8
Subtotal deferred tax assets	513.0	564.5
Deferred tax assets, valuation allowances	(9.6)	(9.2)
Total deferred tax assets	503.4	555.3
Total deferred tax liabilities, net	1,714.0	1,603.1
IPL [Member]
Deferred tax liabilities, property	1,183.5	1,158.4
Deferred tax liabilities, other	76.5	69.4
Total deferred tax liabilities	1,260.0	1,227.8
Deferred tax assets, federal credit carryforwards	175.0	133.2
Deferred tax assets, net operating losses carryforwards - federal	56.3	114.1
Deferred tax assets, net operating losses carryforwards - state	0.6	0.9
Deferred tax assets, other	20.6	22.8
Subtotal deferred tax assets	252.5	271.0
Deferred tax assets, valuation allowances	(0.5)	(0.5)
Total deferred tax assets	252.0	270.5
Total deferred tax liabilities, net	1,008.0	957.3
WPL [Member]
Deferred tax liabilities, property	770.0	735.2
Deferred tax liabilities, other	32.1	34.4
Total deferred tax liabilities	802.1	769.6
Deferred tax assets, federal credit carryforwards	160.3	147.4
Deferred tax assets, net operating losses carryforwards - federal	0.5	26.4
Deferred tax assets, net operating losses carryforwards - state	0.1	0.5
Deferred tax assets, other	15.8	14.1
Subtotal deferred tax assets	176.7	188.4
Deferred tax assets, valuation allowances	(0.8)	(0.8)
Total deferred tax assets	175.9	187.6
Total deferred tax liabilities, net	626.2	582.0
ATC Holdings [Member]
Deferred tax liabilities, ATC Holdings	$ 110.8	$ 102.4