Other Comprehensive Income - Schedule of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Equity [Abstract]
Other comprehensive (loss) income, before tax	$ (621.3)	$ (621.3)	$ (90.4)	$ 61.2
Other Comprehensive Income (Loss), Tax	(155.2)	(155.2)	(22.8)	15.6
Other Comprehensive Income (Loss), Net of Tax	$ (466.1)		(67.6)	45.6
Before Tax Amount
Change in net unrealized loss during period		(613.1)	(113.7)	61.8
Reclassification adjustment for net gains included in net income		24.4	(1.1)	(0.3)
Reclassification adjustment for securities transferred from held-to-maturity to available-for-sale		0.2	0.0	0.0
OCI, Debt Securities, Available-for-Sale, Transfer to Held-to-Maturity, Adjustment from AOCI for Amortization of Gain (Loss), before Tax		(26.1)	20.2	0.0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		(4.9)	3.1	0.2
OCI, Debt Securities, Available-for-Sale, Gain (Loss), before Adjustment, Tax		(6.7)	4.2	0.2
Change in net actuarial gains				(0.5)
Tax Expense (Benefit)
Change in net unrealized loss during period		(152.4)	(28.7)	15.8
Other Comprehensive Income (Loss), Transfers from Held-to-maturity to Available-for-Sale Securities, Tax		0.1
OCI, Debt Securities, Available-for-Sale, Transfer to Held-to-Maturity, Adjustment from AOCI for Amortization of Gain (Loss), Tax		(6.6)	5.1
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax		1.8	(1.1)	0.0
Reclassification adjustment for net gains included in net income		5.5	(0.3)	(0.1)
Change in net actuarial gains				(0.1)
Net of Tax Amount
Change in net unrealized gains during period		(460.7)	(85.0)	46.0
Reclassification adjustment for net gains included in net income		18.9	(0.8)	(0.2)
Other Comprehensive Income (Loss), Transfers from Held-to-maturity to Available-for-Sale Securities, Net of Tax		0.1
OCI, Debt Securities, Available-for-Sale, Transfer to Held-to-Maturity, Adjustment from AOCI for Amortization of Gain (Loss), after Tax		19.5	(15.1)
Change in net actuarial gains				(0.4)
Unrealized Gain (Loss) on Derivatives		(1.6)	3.0
Stockholders' Equity Attributable to Parent		3,073.8	1,986.6	$ 1,959.8	$ 2,013.9
Debt Securities, Held-to-maturity, Transfer, Unrealized Gain (Loss)		$ (4.5)	$ 15.0