Leases (Expected Maturities of Operating and Finance Lease Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Leases [Line Items]
Operating Leases Liability, 2021	$ 2
Operating Leases Liability, 2022	2
Operating Leases Liability, 2023	2
Operating Leases Liability, 2024	2
Operating Leases Liability, 2025	2
Operating Leases Liability, Thereafter	8
Operating Leases Liability, Total	18
Operating Leases Liability, Less: amount representing interest	3
Operating Leases Liability, Present value of minimum lease payments	15	$ 16
IPL [Member]
Leases [Line Items]
Operating Leases Liability, 2021	1
Operating Leases Liability, 2022	1
Operating Leases Liability, 2023	1
Operating Leases Liability, 2024	1
Operating Leases Liability, 2025	1
Operating Leases Liability, Thereafter	6
Operating Leases Liability, Total	11
Operating Leases Liability, Less: amount representing interest	2
Operating Leases Liability, Present value of minimum lease payments	9	10
WPL [Member]
Leases [Line Items]
Operating Leases Liability, 2021	1
Operating Leases Liability, 2022	1
Operating Leases Liability, 2023	1
Operating Leases Liability, 2024	1
Operating Leases Liability, 2025	1
Operating Leases Liability, Thereafter	2
Operating Leases Liability, Total	7
Operating Leases Liability, Less: amount representing interest	1
Operating Leases Liability, Present value of minimum lease payments	6	6
Sheboygan Falls Energy Facility [Member] | WPL [Member]
Leases [Line Items]
Finance Lease Liability, 2021	15
Finance Lease Liability, 2022	15
Finance Lease Liability, 2023	15
Finance Lease Liability, 2024	15
Finance Lease Liability, 2025	5
Finance Lease Liability, Thereafter	0
Finance Lease Liability, Total	65
Finance Lease Liability, Less: amount representing interest	14
Finance Lease Liability, Present value of minimum lease payments	$ 51	$ 60