Derivative Instruments and Hedging Activities - Gains and losses on derivatives (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021
Gains and losses on derivatives
Gain recorded in AOCI on derivatives, net	$ 2.2	$ 6.5
Cash flow hedging | Interest rate swaps
Gains and losses on derivatives
Gain recorded in AOCI on derivatives, before tax	2.9	8.5
Tax impact	(0.7)	(2.0)
Gain recorded in AOCI on derivatives, net	2.2	6.5
Gain (loss) on derivatives	$ (3.8)	$ (9.5)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income	Interest Expense.	Interest Expense.