Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3.0	$ 3.1
Interest cost	11.7	12.8
Expected return on plan assets	(17.4)	(16.4)
Amortization of prior service credit	(0.2)	(0.1)
Amortization of actuarial loss	8.8	9.4
Total	5.9	8.8
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.1	1.2
Interest cost	1.9	2.2
Expected return on plan assets	(1.5)	(1.5)
Amortization of prior service credit	0.0	(0.1)
Amortization of actuarial loss	0.8	1.0
Total	2.3	2.8
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.8	1.8
Interest cost	5.3	5.9
Expected return on plan assets	(8.1)	(7.7)
Amortization of actuarial loss	3.7	4.0
Total	2.7	4.0
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.4	0.5
Interest cost	0.8	0.9
Expected return on plan assets	(1.1)	(1.1)
Amortization of actuarial loss	0.3	0.5
Total	0.4	0.8
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.1	1.2
Interest cost	5.0	5.5
Expected return on plan assets	(7.6)	(7.1)
Amortization of prior service credit	0.0	0.0
Amortization of actuarial loss	4.3	4.6
Total	2.8	4.2
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.4	0.5
Interest cost	0.8	0.9
Expected return on plan assets	(0.2)	(0.2)
Amortization of prior service credit	0.0	(0.1)
Amortization of actuarial loss	0.5	0.4
Total	$ 1.5	$ 1.5