Derivative Instruments and Hedging Activities - Gains and losses on derivatives (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Gains and losses on derivatives
Gain (loss) recorded in AOCL on derivatives, net	$ 4.3	$ (3.0)
Cash flow hedging | Interest rate swaps
Gains and losses on derivatives
Gain (loss) recorded in AOCL on derivatives, before tax	5.6	(3.9)
Tax impact	(1.3)	0.9
Gain (loss) recorded in AOCL on derivatives, net	4.3	(3.0)
Gain (loss) on derivatives	$ (5.7)	$ (3.8)