Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2.5	$ 3.1	$ 7.3	$ 9.1
Interest cost	12.5	11.7	37.4	35.1
Expected return on plan assets	(15.1)	(17.4)	(45.1)	(52.3)
Amortization of prior service credit	(0.2)	(0.2)	(0.5)	(0.5)
Amortization of actuarial loss	9.1	8.8	27.3	26.4
Total	8.8	6.0	26.4	17.8
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.8	1.0	2.5	3.1
Interest cost	2.2	2.0	6.4	5.8
Expected return on plan assets	(1.2)	(1.5)	(3.7)	(4.5)
Amortization of prior service credit	(0.1)	0.0	(0.2)	(0.1)
Amortization of actuarial loss	0.8	0.8	2.4	2.5
Total	2.5	2.3	7.4	6.8
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.6	1.8	4.6	5.5
Interest cost	5.6	5.3	17.0	16.0
Expected return on plan assets	(7.0)	(8.1)	(21.1)	(24.4)
Amortization of prior service credit	(0.1)	0.0	(0.2)	(0.1)
Amortization of actuarial loss	3.9	3.7	11.8	11.2
Total	4.0	2.7	12.1	8.2
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.3	0.4	1.0	1.3
Interest cost	0.8	0.7	2.5	2.3
Expected return on plan assets	(0.9)	(1.1)	(2.7)	(3.3)
Amortization of prior service credit	0.0	0.0	0.0	0.0
Amortization of actuarial loss	0.4	0.4	1.1	1.0
Total	0.6	0.4	1.9	1.3
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.9	1.1	2.6	3.3
Interest cost	5.3	5.0	16.1	15.1
Expected return on plan assets	(6.5)	(7.6)	(19.6)	(22.8)
Amortization of prior service credit	0.0	0.0	(0.1)	(0.1)
Amortization of actuarial loss	4.4	4.3	13.2	12.9
Total	4.1	2.8	12.2	8.4
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.3	0.4	0.9	1.2
Interest cost	0.9	0.8	2.6	2.3
Expected return on plan assets	(0.2)	(0.2)	(0.5)	(0.5)
Amortization of prior service credit	0.0	0.0	(0.1)	(0.1)
Amortization of actuarial loss	0.4	0.5	1.2	1.5
Total	$ 1.4	$ 1.5	$ 4.1	$ 4.4