Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred tax liabilities, property	$ 2,232	$ 2,022
Deferred tax liabilities, other	101	84
Total deferred tax liabilities	2,449	2,217
Deferred tax assets, federal credit carryforwards	454	355
Deferred tax assets, net operating losses carryforwards - federal	77	60
Deferred tax assets, net operating losses carryforwards - state	37	37
Deferred tax assets, other	73	61
Subtotal deferred tax assets	641	513
Deferred tax assets, valuation allowances	(6)	(10)
Total deferred tax assets	635	503
Total deferred tax liabilities, net	1,814	1,714
IPL [Member]
Deferred tax liabilities, property	1,312	1,184
Deferred tax liabilities, other	83	76
Total deferred tax liabilities	1,395	1,260
Deferred tax assets, federal credit carryforwards	258	175
Deferred tax assets, net operating losses carryforwards - federal	71	56
Deferred tax assets, net operating losses carryforwards - state	1	1
Deferred tax assets, other	30	20
Subtotal deferred tax assets	360	252
Deferred tax assets, valuation allowances	0	0
Total deferred tax assets	360	252
Total deferred tax liabilities, net	1,035	1,008
WPL [Member]
Deferred tax liabilities, property	854	770
Deferred tax liabilities, other	41	32
Total deferred tax liabilities	895	802
Deferred tax assets, federal credit carryforwards	175	160
Deferred tax assets, net operating losses carryforwards - federal	1	1
Deferred tax assets, net operating losses carryforwards - state	0	0
Deferred tax assets, other	18	16
Subtotal deferred tax assets	194	177
Deferred tax assets, valuation allowances	(1)	(1)
Total deferred tax assets	193	176
Total deferred tax liabilities, net	702	626
ATC Holdings [Member]
Deferred tax liabilities, ATC Holdings	$ 116	$ 111