Letters of Credit (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Short-term Debt	$ 30.0	$ 150.0
Letter of Credit
Line of Credit Facility [Line Items]
Short-term Debt	10.0	$ 37.0
Bilateral Credit Agreement [Member] | Letter of Credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	75.0
Short-term Debt	22.0
Line of Credit Facility, Remaining Borrowing Capacity	$ 53.0