Leases (Expected Maturities of Operating and Finance Lease Liabilities (Details) $ in Millions	Mar. 31, 2019 USD ($)
Leases [Line Items]
Operating Leases Liability, Remainder of 2019	$ 2
Operating Leases Liability, 2020	2
Operating Leases Liability, 2021	2
Operating Leases Liability, 2022	2
Operating Leases Liability, 2023	2
Operating Leases Liability, Thereafter	13
Operating Leases Liability, Total	23
Operating Leases Liability, Less: amount representing interest	5
Operating Leases Liability, Present value of minimum lease payments	18
IPL [Member]
Leases [Line Items]
Operating Leases Liability, Remainder of 2019	1
Operating Leases Liability, 2020	1
Operating Leases Liability, 2021	1
Operating Leases Liability, 2022	1
Operating Leases Liability, 2023	1
Operating Leases Liability, Thereafter	9
Operating Leases Liability, Total	14
Operating Leases Liability, Less: amount representing interest	4
Operating Leases Liability, Present value of minimum lease payments	10
WPL [Member]
Leases [Line Items]
Operating Leases Liability, Remainder of 2019	1
Operating Leases Liability, 2020	1
Operating Leases Liability, 2021	1
Operating Leases Liability, 2022	1
Operating Leases Liability, 2023	1
Operating Leases Liability, Thereafter	3
Operating Leases Liability, Total	8
Operating Leases Liability, Less: amount representing interest	1
Operating Leases Liability, Present value of minimum lease payments	7
Sheboygan Falls Energy Facility [Member] | WPL [Member]
Leases [Line Items]
Finance Lease Liability, Remainder of 2019	11
Finance Lease Liability, 2020	15
Finance Lease Liability, 2021	15
Finance Lease Liability, 2022	15
Finance Lease Liability, 2023	15
Finance Lease Liability, Thereafter	20
Finance Lease Liability, Total	91
Finance Lease Liability, Less: amount representing interest	25
Finance Lease Liability, Present value of minimum lease payments	$ 66