Borrowings and Other Financing Instruments Borrowings and Other Financing Instruments, Dividend and Other Capital-Related Restrictions (Details) $ in Millions	Dec. 31, 2019 USD ($)
Dividend and Other Capital-Related Restrictions [Abstract]
Minimum calendar year average equity to total capitalization ratio authorized by state commission	51.50%
Equity to total capitalization ratio	51.80%
Unrestricted Retained Earnings Per State Regulatory Commissions Dividend Restrictions	$ 11.5
Capitalization, Short term debt, long term debt and equity	1,800.0
Maximum annual dividends that can be paid if equity capitalization ratio condition is not met	$ 55.0