Benefit Plans (Funded Status of Benefits Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	$ 824	$ 841
Change in benefit obligation:
Net benefit obligation at January 1	841	876
Service cost	4	5	$ 5
Interest cost	46	45	47
Plan participants' contributions	0	0
Actuarial (gain) loss	17	(19)
Gross benefits paid	(84)	(66)
Net benefit obligation at December 31	824	841	876
Change in plan assets:
Fair value of plan assets at January 1	715	732
Actual return on plan assets	93	38
Employer contributions	23	11
Plan participants' contributions	0	0
Gross benefits paid	(84)	(66)
Fair value of plan assets at December 31	747	715	732
Under funded status at December 31	(77)	(126)
Fair value of plan assets	747	715
Pension Plans, Defined Benefit [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	363	372
Change in benefit obligation:
Net benefit obligation at January 1	372	387
Service cost	3	3	3
Interest cost	20	20	21
Plan participants' contributions	0	0
Actuarial (gain) loss	6	(8)
Gross benefits paid	(38)	(30)
Net benefit obligation at December 31	363	372	387
Change in plan assets:
Fair value of plan assets at January 1	340	352
Actual return on plan assets	43	18
Employer contributions	1	0
Plan participants' contributions	0	0
Gross benefits paid	(38)	(30)
Fair value of plan assets at December 31	346	340	352
Under funded status at December 31	(17)	(32)
Fair value of plan assets	346	340
Pension Plans, Defined Benefit [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	362	365
Change in benefit obligation:
Net benefit obligation at January 1	365	381
Service cost	1	2	2
Interest cost	20	20	20
Plan participants' contributions	0	0
Actuarial (gain) loss	9	(8)
Gross benefits paid	(33)	(30)
Net benefit obligation at December 31	362	365	381
Change in plan assets:
Fair value of plan assets at January 1	303	306
Actual return on plan assets	41	17
Employer contributions	16	10
Plan participants' contributions	0	0
Gross benefits paid	(33)	(30)
Fair value of plan assets at December 31	327	303	306
Under funded status at December 31	(35)	(62)
Fair value of plan assets	327	303
Other Postretirement Benefits Plans [Member]
Change in benefit obligation:
Net benefit obligation at January 1	148	160
Service cost	1	2	2
Interest cost	8	8	9
Plan participants' contributions	4	3
Actuarial (gain) loss	6	(7)
Gross benefits paid	(21)	(18)
Net benefit obligation at December 31	146	148	160
Change in plan assets:
Fair value of plan assets at January 1	80	83
Actual return on plan assets	7	5
Employer contributions	8	7
Plan participants' contributions	4	3
Gross benefits paid	(21)	(18)
Fair value of plan assets at December 31	78	80	83
Under funded status at December 31	(68)	(68)
Other Postretirement Benefits Plans [Member] | IPL [Member]
Change in benefit obligation:
Net benefit obligation at January 1	59	65
Service cost	1	1	1
Interest cost	3	3	3
Plan participants' contributions	2	1
Actuarial (gain) loss	3	(3)
Gross benefits paid	(9)	(8)
Net benefit obligation at December 31	59	59	65
Change in plan assets:
Fair value of plan assets at January 1	59	61
Actual return on plan assets	6	4
Employer contributions	2	1
Plan participants' contributions	2	1
Gross benefits paid	(9)	(8)
Fair value of plan assets at December 31	60	59	61
Under funded status at December 31	1	0
Other Postretirement Benefits Plans [Member] | WPL [Member]
Change in benefit obligation:
Net benefit obligation at January 1	56	61
Service cost	1	1	1
Interest cost	3	3	3
Plan participants' contributions	1	1
Actuarial (gain) loss	2	(3)
Gross benefits paid	(8)	(7)
Net benefit obligation at December 31	55	56	61
Change in plan assets:
Fair value of plan assets at January 1	13	14
Actual return on plan assets	2	0
Employer contributions	6	5
Plan participants' contributions	1	1
Gross benefits paid	(8)	(7)
Fair value of plan assets at December 31	14	13	$ 14
Under funded status at December 31	$ (41)	$ (43)