Derivative Instruments and Hedging Activities Open Interest Rate Swap Contracts (Details) - Cash Flow Hedging - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Interest rate swap
Derivative [Line Items]
Notional Amounts	$ 550.0	$ 575.0
Net Unrealized Gain (Loss)	(13.7)	(18.1)
Interest Rate Swap, May 2018 to May 2021
Derivative [Line Items]
Notional Amounts	0.0	25.0
Net Unrealized Gain (Loss)	0.0	(0.2)
Interest Rate Swap, September 2019 to September 2023
Derivative [Line Items]
Notional Amounts	150.0	150.0
Net Unrealized Gain (Loss)	(8.9)	(11.3)
Interest Rate Swap, March 2020 to February 2023
Derivative [Line Items]
Notional Amounts	400.0	400.0
Net Unrealized Gain (Loss)	$ (4.8)	$ (6.6)