Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3.1	$ 3.9	$ 6.3	$ 7.9
Interest cost	13.2	13.4	26.5	26.8
Expected return on plan assets	(16.4)	(18.8)	(32.8)	(37.5)
Amortization of prior service cost (credit)	0.0	0.0	(0.1)	(0.1)
Amortization of actuarial loss	9.4	8.9	18.7	17.7
Additional benefit costs	0.0	0.1	0.0	0.3
Total	9.3	7.5	18.6	15.1
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.3	1.4	2.6	2.8
Interest cost	2.4	2.3	4.7	4.5
Expected return on plan assets	(1.5)	(2.1)	(3.0)	(4.2)
Amortization of prior service cost (credit)	(1.1)	(2.8)	(2.1)	(5.6)
Amortization of actuarial loss	1.2	1.2	2.4	2.4
Additional benefit costs	0.0	0.0	0.0	0.0
Total	2.3	0.0	4.6	(0.1)
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.9	2.2	3.8	4.4
Interest cost	6.2	6.3	12.3	12.5
Expected return on plan assets	(7.8)	(9.0)	(15.5)	(17.9)
Amortization of prior service cost (credit)	(0.1)	(0.1)	(0.1)	(0.1)
Amortization of actuarial loss	4.1	3.9	8.2	7.7
Total	4.3	3.3	8.7	6.6
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.6	0.6	1.2	1.2
Interest cost	0.9	1.0	1.9	1.9
Expected return on plan assets	(1.2)	(1.4)	(2.2)	(2.8)
Amortization of prior service cost (credit)	(0.6)	(1.6)	(1.3)	(3.1)
Amortization of actuarial loss	0.7	0.5	1.3	1.1
Total	0.4	(0.9)	0.9	(1.7)
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.2	1.5	2.4	2.9
Interest cost	5.6	5.7	11.2	11.3
Expected return on plan assets	(7.1)	(8.1)	(14.2)	(16.2)
Amortization of prior service cost (credit)	0.0	0.0	0.1	0.1
Amortization of actuarial loss	4.4	4.2	8.8	8.4
Additional benefit costs	0.0	0.1	0.0	0.3
Total	4.1	3.4	8.3	6.8
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.5	0.5	1.0	1.1
Interest cost	1.0	0.9	1.9	1.8
Expected return on plan assets	(0.2)	(0.4)	(0.4)	(0.8)
Amortization of prior service cost (credit)	(0.2)	(0.8)	(0.4)	(1.7)
Amortization of actuarial loss	0.4	0.5	0.9	1.1
Additional benefit costs	0.0	0.0	0.0	0.0
Total	$ 1.5	$ 0.7	$ 3.0	$ 1.5