Regulatory Assets and Liabilities - Regulatory Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Regulatory liabilities
Other current liabilities	$ 51.0	$ 87.6
Regulatory liabilities	3,928.1	3,992.8
Total regulatory liabilities	3,979.1	4,080.4
Income tax related items
Regulatory liabilities
Total regulatory liabilities	2,137.7	2,248.8
Removal costs
Regulatory liabilities
Total regulatory liabilities	1,221.1	1,181.5
Pension and OPEB benefits
Regulatory liabilities
Total regulatory liabilities	378.1	354.9
Electric transmission costs
Regulatory liabilities
Total regulatory liabilities	78.5	42.2
Earnings sharing refunds offsetting electric transmission regulatory liability		38.6
Energy costs refundable through rate adjustments
Regulatory liabilities
Total regulatory liabilities	59.9	89.8
Earnings sharing mechanisms
Regulatory liabilities
Total regulatory liabilities	36.9	43.5
Earnings sharing mechanisms | WE
Regulatory liabilities
Total regulatory liabilities	0.0
Uncollectible expense
Regulatory liabilities
Total regulatory liabilities	25.5	39.1
Derivatives
Regulatory liabilities
Total regulatory liabilities	16.4	6.7
Energy efficiency programs
Regulatory liabilities
Total regulatory liabilities	9.9	30.7
Decoupling
Regulatory liabilities
Total regulatory liabilities	5.2	36.8
Other, net
Regulatory liabilities
Total regulatory liabilities	$ 9.9	$ 6.4