Investment Securities - Gross Unrealized Losses and Fair Values of Investment Securities (Details) - USD ($)
$ in Millions |
3 Months Ended |
6 Months Ended |
|
Mar. 31, 2025 |
Jun. 30, 2025 |
Dec. 31, 2024 |
| Available-for-Sale: |
|
|
|
| Fair Value, Less than 12 Months |
|
$ 53.7
|
$ 133.4
|
| Gross Unrealized Losses, Less than 12 Months |
|
(0.6)
|
(2.7)
|
| Fair Value, 12 Months or Longer |
|
3,877.3
|
4,047.2
|
| Gross Unrealized Losses, 12 Months or Longer |
|
(306.3)
|
(417.4)
|
| Fair Value, Total |
|
3,931.0
|
4,180.6
|
| Gross Unrealized Losses, Total |
|
(306.9)
|
(420.1)
|
| Allowance for Credit Losses |
|
0.0
|
|
| Gross Unrealized Gains |
|
4.6
|
2.4
|
| Gross Unrealized Losses |
|
(306.9)
|
(420.1)
|
| Debt Securities, Available-for-Sale, Excluding Accrued Interest |
|
4,742.2
|
5,057.1
|
| Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss |
|
5,044.5
|
5,474.8
|
| Investment securities classified as held to maturity |
|
2,570.7
|
2,688.4
|
| Allowance for Credit Losses |
|
(0.7)
|
(0.9)
|
| Net Amortized Cost |
|
2,570.0
|
2,687.5
|
| Gross Unrealized Gains |
|
0.9
|
0.2
|
| Gross Unrealized Losses |
|
(254.6)
|
(330.0)
|
| Investment debt securities held-to-maturity |
|
2,317.0
|
2,358.6
|
| Debt Securities, Held-To-Maturity, Transfer, Unamortized Loss |
$ 15.9
|
|
|
| Debt Securities, Held-To-Maturity, Transfer, Unamortized Gain |
$ (8.0)
|
|
|
| US Treasury Notes Securities |
|
|
|
| Available-for-Sale: |
|
|
|
| Fair Value, Less than 12 Months |
|
0.0
|
|
| Gross Unrealized Losses, Less than 12 Months |
|
0.0
|
|
| Fair Value, 12 Months or Longer |
|
233.9
|
|
| Gross Unrealized Losses, 12 Months or Longer |
|
(11.8)
|
|
| Fair Value, Total |
|
233.9
|
|
| Gross Unrealized Losses, Total |
|
(11.8)
|
|
| U.S. Treasury notes |
|
|
|
| Available-for-Sale: |
|
|
|
| Fair Value, Less than 12 Months |
|
|
0.0
|
| Gross Unrealized Losses, Less than 12 Months |
|
|
0.0
|
| Fair Value, 12 Months or Longer |
|
|
226.8
|
| Gross Unrealized Losses, 12 Months or Longer |
|
|
(18.1)
|
| Fair Value, Total |
|
|
226.8
|
| Gross Unrealized Losses, Total |
|
|
(18.1)
|
| Gross Unrealized Gains |
|
0.0
|
0.0
|
| Gross Unrealized Losses |
|
(11.8)
|
(18.1)
|
| Debt Securities, Available-for-Sale, Excluding Accrued Interest |
|
233.9
|
226.9
|
| Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss |
|
245.7
|
245.0
|
| Investment securities classified as held to maturity |
|
100.0
|
99.8
|
| Gross Unrealized Gains |
|
0.0
|
0.0
|
| Gross Unrealized Losses |
|
(0.1)
|
(0.4)
|
| Investment debt securities held-to-maturity |
|
99.9
|
99.4
|
| State, county, and municipal securities |
|
|
|
| Available-for-Sale: |
|
|
|
| Fair Value, Less than 12 Months |
|
0.0
|
0.0
|
| Gross Unrealized Losses, Less than 12 Months |
|
0.0
|
0.0
|
| Fair Value, 12 Months or Longer |
|
211.6
|
210.1
|
| Gross Unrealized Losses, 12 Months or Longer |
|
(35.8)
|
(40.0)
|
| Fair Value, Total |
|
211.6
|
210.1
|
| Gross Unrealized Losses, Total |
|
(35.8)
|
(40.0)
|
| Gross Unrealized Gains |
|
0.0
|
0.0
|
| Gross Unrealized Losses |
|
(35.8)
|
(40.0)
|
| Debt Securities, Available-for-Sale, Excluding Accrued Interest |
|
213.4
|
212.0
|
| Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss |
|
249.2
|
252.0
|
| Investment securities classified as held to maturity |
|
175.8
|
176.3
|
| Gross Unrealized Gains |
|
0.2
|
0.2
|
| Gross Unrealized Losses |
|
(23.5)
|
(26.7)
|
| Investment debt securities held-to-maturity |
|
152.5
|
149.8
|
| Obligations of U.S. government agencies |
|
|
|
| Available-for-Sale: |
|
|
|
| Fair Value, Less than 12 Months |
|
1.0
|
3.6
|
| Gross Unrealized Losses, Less than 12 Months |
|
0.0
|
0.0
|
| Fair Value, 12 Months or Longer |
|
200.7
|
206.2
|
| Gross Unrealized Losses, 12 Months or Longer |
|
(6.5)
|
(10.8)
|
| Fair Value, Total |
|
201.7
|
209.8
|
| Gross Unrealized Losses, Total |
|
(6.5)
|
(10.8)
|
| Gross Unrealized Gains |
|
0.0
|
0.0
|
| Gross Unrealized Losses |
|
(6.5)
|
(10.8)
|
| Debt Securities, Available-for-Sale, Excluding Accrued Interest |
|
206.7
|
213.3
|
| Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss |
|
213.2
|
224.1
|
| Investment securities classified as held to maturity |
|
466.8
|
470.1
|
| Gross Unrealized Gains |
|
0.0
|
0.0
|
| Gross Unrealized Losses |
|
(45.2)
|
(59.9)
|
| Investment debt securities held-to-maturity |
|
421.6
|
410.2
|
| Private mortgage-backed securities |
|
|
|
| Available-for-Sale: |
|
|
|
| Fair Value, Less than 12 Months |
|
0.0
|
0.0
|
| Gross Unrealized Losses, Less than 12 Months |
|
0.0
|
0.0
|
| Fair Value, 12 Months or Longer |
|
182.2
|
190.4
|
| Gross Unrealized Losses, 12 Months or Longer |
|
(23.2)
|
(27.6)
|
| Fair Value, Total |
|
182.2
|
190.4
|
| Gross Unrealized Losses, Total |
|
(23.2)
|
(27.6)
|
| Gross Unrealized Gains |
|
0.0
|
0.0
|
| Gross Unrealized Losses |
|
(23.2)
|
(27.6)
|
| Debt Securities, Available-for-Sale, Excluding Accrued Interest |
|
182.3
|
190.5
|
| Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss |
|
205.5
|
218.1
|
| Collateralized Loan Obligations |
|
|
|
| Available-for-Sale: |
|
|
|
| Fair Value, Less than 12 Months |
|
|
10.0
|
| Gross Unrealized Losses, Less than 12 Months |
|
|
0.0
|
| Fair Value, 12 Months or Longer |
|
|
0.0
|
| Gross Unrealized Losses, 12 Months or Longer |
|
|
0.0
|
| Fair Value, Total |
|
|
10.0
|
| Gross Unrealized Losses, Total |
|
|
0.0
|
| Gross Unrealized Gains |
|
1.0
|
1.3
|
| Gross Unrealized Losses |
|
0.0
|
0.0
|
| Debt Securities, Available-for-Sale, Excluding Accrued Interest |
|
626.8
|
772.0
|
| Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss |
|
625.8
|
770.7
|
| Corporate Debt Securities |
|
|
|
| Available-for-Sale: |
|
|
|
| Fair Value, Less than 12 Months |
|
13.0
|
27.5
|
| Gross Unrealized Losses, Less than 12 Months |
|
0.0
|
(0.5)
|
| Fair Value, 12 Months or Longer |
|
192.1
|
205.5
|
| Gross Unrealized Losses, 12 Months or Longer |
|
(12.0)
|
(16.2)
|
| Fair Value, Total |
|
205.1
|
233.0
|
| Gross Unrealized Losses, Total |
|
(12.0)
|
(16.7)
|
| Gross Unrealized Gains |
|
0.0
|
0.0
|
| Gross Unrealized Losses |
|
(12.0)
|
(16.7)
|
| Debt Securities, Available-for-Sale, Excluding Accrued Interest |
|
227.0
|
232.9
|
| Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss |
|
239.0
|
249.6
|
| Investment securities classified as held to maturity |
|
40.0
|
57.0
|
| Gross Unrealized Gains |
|
0.0
|
0.0
|
| Gross Unrealized Losses |
|
(1.8)
|
(2.8)
|
| Investment debt securities held-to-maturity |
|
38.2
|
54.2
|
| Commercial Mortgage-Backed Securities |
|
|
|
| Available-for-Sale: |
|
|
|
| Fair Value, Less than 12 Months |
|
0.0
|
38.1
|
| Gross Unrealized Losses, Less than 12 Months |
|
0.0
|
(0.4)
|
| Fair Value, 12 Months or Longer |
|
898.0
|
934.9
|
| Gross Unrealized Losses, 12 Months or Longer |
|
(49.6)
|
(74.1)
|
| Fair Value, Total |
|
898.0
|
973.0
|
| Gross Unrealized Losses, Total |
|
(49.6)
|
(74.5)
|
| Gross Unrealized Gains |
|
1.0
|
0.1
|
| Gross Unrealized Losses |
|
(49.6)
|
(74.5)
|
| Debt Securities, Available-for-Sale, Excluding Accrued Interest |
|
947.1
|
982.8
|
| Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss |
|
995.7
|
1,057.2
|
| Investment securities classified as held to maturity |
|
369.7
|
374.9
|
| Gross Unrealized Gains |
|
0.0
|
0.0
|
| Gross Unrealized Losses |
|
(24.8)
|
(33.4)
|
| Investment debt securities held-to-maturity |
|
344.9
|
341.5
|
| Residential Mortgage Backed Securities |
|
|
|
| Available-for-Sale: |
|
|
|
| Fair Value, Less than 12 Months |
|
32.9
|
33.7
|
| Gross Unrealized Losses, Less than 12 Months |
|
(0.6)
|
(1.5)
|
| Fair Value, 12 Months or Longer |
|
1,022.3
|
1,086.2
|
| Gross Unrealized Losses, 12 Months or Longer |
|
(87.4)
|
(124.3)
|
| Fair Value, Total |
|
1,055.2
|
1,119.9
|
| Gross Unrealized Losses, Total |
|
(88.0)
|
(125.8)
|
| Gross Unrealized Gains |
|
1.2
|
0.4
|
| Gross Unrealized Losses |
|
(88.0)
|
(125.8)
|
| Debt Securities, Available-for-Sale, Excluding Accrued Interest |
|
1,111.4
|
1,175.8
|
| Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss |
|
1,198.2
|
1,301.2
|
| Investment securities classified as held to maturity |
|
1,013.4
|
1,082.5
|
| Gross Unrealized Gains |
|
0.2
|
0.0
|
| Gross Unrealized Losses |
|
(105.1)
|
(140.7)
|
| Investment debt securities held-to-maturity |
|
908.5
|
941.8
|
| Collateralized Mortgage Obligations |
|
|
|
| Available-for-Sale: |
|
|
|
| Fair Value, Less than 12 Months |
|
6.8
|
20.5
|
| Gross Unrealized Losses, Less than 12 Months |
|
0.0
|
(0.3)
|
| Fair Value, 12 Months or Longer |
|
936.5
|
987.1
|
| Gross Unrealized Losses, 12 Months or Longer |
|
(80.0)
|
(106.3)
|
| Fair Value, Total |
|
943.3
|
1,007.6
|
| Gross Unrealized Losses, Total |
|
(80.0)
|
(106.6)
|
| Gross Unrealized Gains |
|
1.4
|
0.6
|
| Gross Unrealized Losses |
|
(80.0)
|
(106.6)
|
| Debt Securities, Available-for-Sale, Excluding Accrued Interest |
|
993.6
|
1,050.9
|
| Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss |
|
1,072.2
|
1,156.9
|
| Investment securities classified as held to maturity |
|
405.0
|
427.8
|
| Gross Unrealized Gains |
|
0.5
|
0.0
|
| Gross Unrealized Losses |
|
(54.1)
|
(66.1)
|
| Investment debt securities held-to-maturity |
|
351.4
|
$ 361.7
|
| US agency, residential and commercial MBS and CMOs |
|
|
|
| Available-for-Sale: |
|
|
|
| Debt Securities, Held-To-Maturity, Transfer, Unamortized Gain |
|
(6.9)
|
|
| State, county & municipal, obligations of US govt agencies and CLOs |
|
|
|
| Available-for-Sale: |
|
|
|
| Debt Securities, Held-To-Maturity, Transfer, Unamortized Loss |
|
$ 14.8
|
|