Derivative Financial Instruments and Hedging Activities - Schedule of Fair Value by Balance Sheet Location (Details) - Not Designated as Hedging Instrument - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Derivative Asset, Fair Value, Gross	$ 284.2	$ 326.1
Cash collateral	28.9	18.2
Derivative Asset, Fair Value, Gross, Total net of cash collateral	255.3	307.9
Derivative Liabilities, Fair Value, Gross	249.8	310.5
Cash collateral	25.1	38.6
Derivative Liabilities, Fair Value, Gross, Total net of cash collateral	224.7	271.9
Derivative Asset	142.0	155.8
Derivative Assets, Total net of cash collateral	113.1	137.6
Derivative Liabilities, Fair Value, Net	107.9	140.3
Derivative Liabilities, Total net of cash collateral	$ 82.8	$ 101.7