Leases (Operating Leases) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Leases [Line Items]
Operating leases assets, Property, plant and equipment, net	$ 18
Operating leases liabilities, Other current liabilities	3
Operating leases liabilities, Other liabilities	15
Operating leases liabilities, Total	18
Operating leases, Cost	$ 1
Operating leases, Weighted average remaining lease term	12 years
Operating leases, Weighted average discount rate, percent	4.00%
IPL [Member]
Leases [Line Items]
Operating leases assets, Property, plant and equipment, net	$ 10
Operating leases liabilities, Other current liabilities	1
Operating leases liabilities, Other liabilities	9
Operating leases liabilities, Total	10
Operating leases, Cost	$ 0
Operating leases, Weighted average remaining lease term	13 years
Operating leases, Weighted average discount rate, percent	4.00%
WPL [Member]
Leases [Line Items]
Operating leases assets, Property, plant and equipment, net	$ 7
Operating leases liabilities, Other current liabilities	1
Operating leases liabilities, Other liabilities	6
Operating leases liabilities, Total	7
Operating leases, Cost	$ 0
Operating leases, Weighted average remaining lease term	10 years
Operating leases, Weighted average discount rate, percent	4.00%