Derivatives and Hedging Activities - Schedule of Master Netting Arrangements (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Derivative Asset [Abstract]
Derivative Asset, Fair Value, Gross Asset	$ 28.1	$ 55.3
Derivative Asset, Fair Value, Gross Liability	0.0	0.0
Derivative Asset, Total	28.1	55.3
Derivative, Collateral, Obligation to Return Securities	0.0	0.0
Derivative, Collateral, Obligation to Return Cash	8.0	17.2
Derivative Asset, Fair Value, Amount Offset Against Collateral, Total	20.1	38.1
Offsetting Derivative Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	18.2	17.9
Derivative Liability, Fair Value, Gross Asset	0.0	0.0
Derivative Liability, Total	18.2	17.9
Derivative, Collateral, Right to Reclaim Securities	0.0	0.0
Derivative, Collateral, Right to Reclaim Cash	0.0	0.0
Derivative Liability, Fair Value, Amount Offset Against Collateral, Total	18.2	17.9
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral [Abstract]
Securities Sold under Agreements to Repurchase, Gross	1,051.1	1,091.4
Securities Sold under Agreements to Repurchase, Asset	0.0	0.0
Securities Sold under Agreements to Repurchase, Total	1,051.1	1,091.4
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities	0.0	0.0
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Cash	1,051.1	1,091.4
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral, Total	0.0	0.0
Offsetting Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned [Abstract]
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Gross	1,069.3	1,109.3
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Asset	0.0	0.0
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Total	1,069.3	1,109.3
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Collateral, Right to Reclaim Securities	0.0	0.0
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Collateral, Right to Reclaim Cash	1,051.1	1,091.4
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Amount Offset Against Collateral, Total	18.2	17.9
Derivative Asset, Notional Amount	1,691.2	901.6
Derivative Assets, Estimated Fair Value	28.1	55.3
Derivative Liability, Notional Amount	1,103.9	1,014.1
Derivative Liabilities, Estimated Fair Value	18.2	17.9
Collateral Pledged
Offsetting Derivative Liabilities [Abstract]
Derivative, Collateral, Right to Reclaim Securities	0.2
Offsetting Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned [Abstract]
Derivative, Fair Value, Net	7.8
Interest Rate Swap [Member]
Derivative Asset [Abstract]
Derivative Asset, Fair Value, Gross Asset	26.3	52.0
Derivative Asset, Fair Value, Gross Liability	0.0	0.0
Derivative Asset, Total	26.3	52.0
Derivative, Collateral, Obligation to Return Securities	0.0	0.0
Derivative, Collateral, Obligation to Return Cash	8.0	17.2
Derivative Asset, Fair Value, Amount Offset Against Collateral, Total	18.3	34.8
Offsetting Derivative Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	18.2	16.8
Derivative Liability, Fair Value, Gross Asset	0.0	0.0
Derivative Liability, Total	18.2	16.8
Derivative, Collateral, Right to Reclaim Securities	0.0	0.0
Derivative, Collateral, Right to Reclaim Cash	0.0	0.0
Derivative Liability, Fair Value, Amount Offset Against Collateral, Total	18.2	16.8
Interest Rate Swap [Member] | Not Designated as Hedging Instrument
Offsetting Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned [Abstract]
Derivative Asset, Notional Amount	913.9	799.7
Derivative Assets, Estimated Fair Value	22.2	52.0
Derivative Liability, Notional Amount	913.9	799.7
Derivative Liabilities, Estimated Fair Value	18.1	16.6
Interest Rate Swap [Member] | Designated as Hedging Instrument
Offsetting Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned [Abstract]
Derivative Asset, Notional Amount	700.0	0.0
Derivative Assets, Estimated Fair Value	4.1	0.0
Derivative Liability, Notional Amount	87.6	87.6
Derivative Liabilities, Estimated Fair Value	0.1	0.2
Mortgage related derivatives
Derivative Asset [Abstract]
Derivative Asset, Fair Value, Gross Asset	1.8	3.3
Derivative Asset, Fair Value, Gross Liability	0.0	0.0
Derivative Asset, Total	1.8	3.3
Derivative, Collateral, Obligation to Return Securities	0.0	0.0
Derivative, Collateral, Obligation to Return Cash	0.0	0.0
Derivative Asset, Fair Value, Amount Offset Against Collateral, Total	$ 1.8	3.3
Offsetting Derivative Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability		1.1
Derivative Liability, Fair Value, Gross Asset		0.0
Derivative Liability, Total		1.1
Derivative, Collateral, Right to Reclaim Securities		0.0
Derivative, Collateral, Right to Reclaim Cash		0.0
Derivative Liability, Fair Value, Amount Offset Against Collateral, Total		$ 1.1