Leases (Operating Leases) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Leases [Line Items]
Operating leases assets, Property, plant and equipment, net	$ 15	$ 16
Operating leases liabilities, Other current liabilities	2	2
Operating leases liabilities, Other liabilities	13	14
Operating leases liabilities, Total	$ 15	$ 16
Operating leases, Weighted average remaining lease term	10 years	11 years
Operating leases, Weighted average discount rate, percent	4.00%	4.00%
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent
IPL [Member]
Leases [Line Items]
Operating leases assets, Property, plant and equipment, net	$ 9	$ 10
Operating leases liabilities, Other current liabilities	1	1
Operating leases liabilities, Other liabilities	8	9
Operating leases liabilities, Total	$ 9	$ 10
Operating leases, Weighted average remaining lease term	11 years	12 years
Operating leases, Weighted average discount rate, percent	4.00%	4.00%
WPL [Member]
Leases [Line Items]
Operating leases assets, Property, plant and equipment, net	$ 6	$ 6
Operating leases liabilities, Other current liabilities	1	1
Operating leases liabilities, Other liabilities	5	5
Operating leases liabilities, Total	$ 6	$ 6
Operating leases, Weighted average remaining lease term	9 years	10 years
Operating leases, Weighted average discount rate, percent	4.00%	4.00%