Borrowings and Other Financing Instruments Borrowings and Other Financing Instruments, Long-Term Borrowings and Other Financing Instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Long-Term Borrowings and Other Financing Instruments
Unamortized discount	$ (3)	$ (3)
Unamortized debt expense	(9)	(7)
Less current maturities	0	(151)
Long-term debt, noncurrent	807	610
2019	0
2020	0
2021	19
2022	0
2023	0
First Mortgage Bonds
Long-Term Borrowings and Other Financing Instruments
Long-term Debt, Gross	$ 800	750
Debt Instrument, Maturity Date Range, Start	Jun. 15, 2024
Debt Instrument, Maturity Date Range, End	Sep. 01, 2048
City of La Crosse Resource Recovery Bond
Long-Term Borrowings and Other Financing Instruments
Long-term Debt, Gross	$ 19	$ 19
Debt Instrument, Interest Rate, Stated Percentage	6.00%	6.00%
Debt Instrument, Maturity Date	Nov. 01, 2021
Other
Long-Term Borrowings and Other Financing Instruments
Long-term Debt, Gross	$ 0	$ 2
Series Due December 1, 2047 [Member] | First Mortgage Bonds
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage		3.75%
Debt Instrument, Face Amount		$ 100
Debt Instrument, Maturity Date		Dec. 01, 2047
Series Due December 1, 2048 [Member] | First Mortgage Bonds
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	4.20%
Debt Instrument, Face Amount	$ 200
Debt Instrument, Maturity Date	Sep. 01, 2048
Minimum | First Mortgage Bonds
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	3.30%	3.30%
Maximum | First Mortgage Bonds
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	6.375%	6.375%