Debt Securities, Held-To-Maturity, Transfer, Unamortized Gain

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Debt Securities, Held-To-Maturity, Transfer, Unamortized Loss

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount excluding accrued interest, of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost excluding accrued interest, after allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of allowance for credit loss for debt security measured at amortized cost (held-to-maturity).

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Amount, after allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

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Amount, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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Investment Securities - Amortized Cost and Approximate Fair Values of Investment Securities (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
Available-for-Sale:
Gross Unrealized Gains	$ 0.2			$ 2.3
Gross Unrealized Losses	(590.5)			(629.7)
Held-to-Maturity:
Investment securities classified as held to maturity	3,318.4			3,453.7
Allowance for Credit Losses	(0.7)	$ (1.6)	$ (0.7)	(1.9)	$ (1.6)	$ 0.0
Net Amortized Cost	3,317.7			3,451.8
Gross Unrealized Gains	0.4			0.4
Gross Unrealized Losses	(393.4)			(400.0)
Investment debt securities held-to-maturity	2,924.7			3,052.2
Estimated Fair Value	5,857.9			6,946.1
Debt Securities, Available-for-Sale, Amortized Cost, after Allowance for Credit Loss	6,448.2			7,573.5
Allowance for Credit Losses	(1.4)	0.0	$ (2.6)	0.0	$ 0.0	$ 0.0
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	6,449.6			7,573.5
U.S. Treasury notes
Available-for-Sale:
Gross Unrealized Gains	0.0			2.1
Gross Unrealized Losses	(31.0)			(34.5)
Held-to-Maturity:
Investment securities classified as held to maturity	397.8			396.6
Allowance for Credit Losses	0.0			0.0
Net Amortized Cost	397.8			396.6
Gross Unrealized Gains	0.0			0.0
Gross Unrealized Losses	(8.9)			(10.2)
Investment debt securities held-to-maturity	388.9			386.4
Estimated Fair Value	219.1			642.7
Debt Securities, Available-for-Sale, Amortized Cost, after Allowance for Credit Loss	250.1			675.1
Allowance for Credit Losses	0.0			0.0
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	250.1			675.1
State, county, and municipal securities
Available-for-Sale:
Gross Unrealized Gains	0.0			0.0
Gross Unrealized Losses	(43.2)			(50.6)
Held-to-Maturity:
Investment securities classified as held to maturity	180.5			181.2
Allowance for Credit Losses	0.0			(0.1)
Net Amortized Cost	180.5			181.1
Gross Unrealized Gains	0.2			0.2
Gross Unrealized Losses	(27.0)			(31.6)
Investment debt securities held-to-maturity	153.7			149.7
Estimated Fair Value	214.9			263.7
Debt Securities, Available-for-Sale, Amortized Cost, after Allowance for Credit Loss	258.1			314.3
Allowance for Credit Losses	0.0			0.0
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	258.1			314.3
Obligations of U.S. government agencies
Available-for-Sale:
Gross Unrealized Gains	0.0			0.0
Gross Unrealized Losses	(14.4)			(17.3)
Held-to-Maturity:
Investment securities classified as held to maturity	353.1			351.7
Allowance for Credit Losses	0.0			0.0
Net Amortized Cost	353.1			351.7
Gross Unrealized Gains	0.0			0.0
Gross Unrealized Losses	(48.9)			(49.6)
Investment debt securities held-to-maturity	304.2			302.1
Estimated Fair Value	172.0			198.9
Debt Securities, Available-for-Sale, Amortized Cost, after Allowance for Credit Loss	186.4			216.2
Allowance for Credit Losses	0.0			0.0
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	186.4			216.2
U.S. agency commercial mortgage-backed securities
Held-to-Maturity:
Debt Securities, Held-To-Maturity, Transfer, Unamortized Gain	12.3	$ 20.1
Debt Securities, Held-To-Maturity, Transfer, Unamortized Loss	(19.2)
Corporate Debt Securities
Available-for-Sale:
Gross Unrealized Gains	0.0			0.0
Gross Unrealized Losses	(32.6)			(30.8)
Held-to-Maturity:
Investment securities classified as held to maturity	57.1			80.1
Allowance for Credit Losses	(0.7)			(1.8)
Net Amortized Cost	56.4			78.3
Gross Unrealized Gains	0.0			0.0
Gross Unrealized Losses	(7.8)			(7.0)
Investment debt securities held-to-maturity	48.6			71.3
Estimated Fair Value	227.5			241.5
Debt Securities, Available-for-Sale, Amortized Cost, after Allowance for Credit Loss	260.1			272.3
Allowance for Credit Losses	(1.4)			0.0
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	261.5			272.3
Collateralized Mortgage Obligations
Available-for-Sale:
Gross Unrealized Gains	0.0			0.0
Gross Unrealized Losses	(145.6)			(141.3)
Held-to-Maturity:
Investment securities classified as held to maturity	500.7			525.8
Allowance for Credit Losses	0.0			0.0
Net Amortized Cost	500.7			525.8
Gross Unrealized Gains	0.2			0.2
Gross Unrealized Losses	(78.7)			(76.7)
Investment debt securities held-to-maturity	422.2			449.3
Estimated Fair Value	1,205.2			1,350.2
Debt Securities, Available-for-Sale, Amortized Cost, after Allowance for Credit Loss	1,350.8			1,491.5
Allowance for Credit Losses	0.0			0.0
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	1,350.8			1,491.5
Commercial Mortgage-Backed Securities
Available-for-Sale:
Gross Unrealized Gains	0.2			0.2
Gross Unrealized Losses	(110.7)			(117.0)
Held-to-Maturity:
Investment securities classified as held to maturity	517.8			526.8
Allowance for Credit Losses	0.0			0.0
Net Amortized Cost	517.8			526.8
Gross Unrealized Gains	0.0			0.0
Gross Unrealized Losses	(61.4)			(58.3)
Investment debt securities held-to-maturity	456.4			468.5
Estimated Fair Value	1,102.4			1,351.2
Debt Securities, Available-for-Sale, Amortized Cost, after Allowance for Credit Loss	1,212.9			1,468.0
Allowance for Credit Losses	0.0			0.0
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	1,212.9			1,468.0
Residential Mortgage Backed Securities
Available-for-Sale:
Gross Unrealized Gains	0.0			0.0
Gross Unrealized Losses	(159.1)			(167.7)
Held-to-Maturity:
Investment securities classified as held to maturity	1,311.4			1,391.5
Allowance for Credit Losses	0.0			0.0
Net Amortized Cost	1,311.4			1,391.5
Gross Unrealized Gains	0.0			0.0
Gross Unrealized Losses	(160.7)			(166.6)
Investment debt securities held-to-maturity	1,150.7			1,224.9
Estimated Fair Value	1,375.4			1,558.3
Debt Securities, Available-for-Sale, Amortized Cost, after Allowance for Credit Loss	1,534.5			1,726.0
Allowance for Credit Losses	0.0			0.0
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	1,534.5			1,726.0
Other investments
Available-for-Sale:
Gross Unrealized Gains	0.0			0.0
Gross Unrealized Losses	0.0			0.0
Held-to-Maturity:
Estimated Fair Value	0.0			0.0
Debt Securities, Available-for-Sale, Amortized Cost, after Allowance for Credit Loss				0.0
Allowance for Credit Losses	0.0			0.0
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	0.0			0.0
Private mortgage-backed securities
Available-for-Sale:
Gross Unrealized Gains	0.0			0.0
Gross Unrealized Losses	(36.4)			(36.9)
Held-to-Maturity:
Estimated Fair Value	217.1			228.0
Debt Securities, Available-for-Sale, Amortized Cost, after Allowance for Credit Loss	253.5			264.9
Allowance for Credit Losses	0.0			0.0
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	253.5			264.9
Collateralized Loan Obligations
Available-for-Sale:
Gross Unrealized Gains	0.0			0.0
Gross Unrealized Losses	(17.5)			(33.6)
Held-to-Maturity:
Estimated Fair Value	1,124.3			1,111.6
Debt Securities, Available-for-Sale, Amortized Cost, after Allowance for Credit Loss	1,141.8			1,145.2
Allowance for Credit Losses	0.0			0.0
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	$ 1,141.8			$ 1,145.2