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Regulatory Capital - Schedule of Actual Capital Amounts and Ratios and Selected Minimum Regulatory Thresholds (Details) $ in Millions | Jan. 01, 2020 USD ($) | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($)
--- | --- | --- | ---
Total risk-based capital: |  |  |
Actual amount |  | $ 2,941.1 | $ 2,875.8
Capital to Risk Weighted Assets |  | 0.1328 | 0.1248
Adequately capitalized Basel III phase-in schedule, amount |  | $ 1,771.6 | $ 1,843.2
Adequately capitalized Basel III phase-in schedule, ratio (percent) |  | 0.0800 | 0.0800
Adequately capitalized Basel III fully phased-in, amount |  | $ 2,325.2 | $ 2,419.2
Capital Required For Capital Adequacy Under Basel III Fully Phased-In To Risk Weighted Assets |  | 10.50% | 10.50%
Well capitalized, amount |  | $ 2,214.5 | $ 2,304.0
Capital Required to be Well Capitalized to Risk Weighted Assets |  | 0.1000 | 0.1000
Tier 1 risk-based capital: |  |  |
Actual amount |  | $ 2,454.4 | $ 2,408.8
Tier One Risk Based Capital to Risk Weighted Assets |  | 0.1108 | 0.1045
Adequately capitalized Basel III phase-in schedule, amount |  | $ 1,328.7 | $ 1,382.4
Adequately capitalized Basel III phase-in schedule, ratio (percent) |  | 0.0600 | 0.0600
Adequately capitalized Basel III fully phased-in, amount |  | $ 1,882.3 | $ 1,958.4
Tier One Capital Required For Capital Adequacy Under Basel III Fully Phased-In To Risk Weighted Assets |  | 8.50% | 8.50%
Well capitalized, amount |  | $ 1,771.6 | $ 1,843.2
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets |  | 0.0800 | 0.0800
Common Equity Tier One Capital [Abstract] |  |  |
Actual amount |  | $ 2,454.4 | $ 2,408.8
Common Equity Tier One Risk Based Capital To Risk Weighted Assets |  | 11.08% | 10.45%
Adequately capitalized Basel III phase-in schedule, amount |  | $ 996.5 | $ 1,036.8
Adequately capitalized Basel III phase-in schedule, ratio (percent) |  | 4.50% | 4.50%
Adequately capitalized Basel III fully phased-in, amount |  | $ 1,550.1 | $ 1,612.8
Tier One Common Equity Capital Required For Capital Adequacy Under Basel III Fully Phased-In To Risk Weighted Assets |  | 7.00% | 7.00%
Well capitalized, amount |  | $ 1,439.4 | $ 1,497.6
Common Equity Tier One Capital To Be Well Capitalized To Risk Weighted Assets |  | 6.50% | 6.50%
Leverage capital ratio: |  |  |
Actual amount |  | $ 2,454.4 | $ 2,408.8
Tier One Leverage Capital to Average Assets |  | 0.0822 | 0.0775
Adequately capitalized, amount |  | $ 1,193.9 | $ 1,242.9
Adequately capitalized, ratio (percent) |  | 0.0400 | 0.0400
Well capitalized, amount |  | $ 1,492.3 | $ 1,553.6
Well capitalized, ratio (percent) |  | 0.0500 | 0.0500
Income Tax Effects Allocated Directly to Equity, Cumulative Effect of Change in Accounting Principle | $ 24.1 |  |
FIB |  |  |
Total risk-based capital: |  |  |
Actual amount |  | $ 2,662.0 | $ 2,713.5
Capital to Risk Weighted Assets |  | 0.1204 | 0.1180
Adequately capitalized Basel III phase-in schedule, amount |  | $ 1,768.3 | $ 1,839.6
Adequately capitalized Basel III phase-in schedule, ratio (percent) |  | 0.0800 | 0.0800
Adequately capitalized Basel III fully phased-in, amount |  | $ 2,320.8 | $ 2,414.5
Capital Required For Capital Adequacy Under Basel III Fully Phased-In To Risk Weighted Assets |  | 10.50% | 10.50%
Well capitalized, amount |  | $ 2,210.3 | $ 2,299.5
Capital Required to be Well Capitalized to Risk Weighted Assets |  | 0.1000 | 0.1000
Tier 1 risk-based capital: |  |  |
Actual amount |  | $ 2,433.0 | $ 2,504.1
Tier One Risk Based Capital to Risk Weighted Assets |  | 0.1101 | 0.1089
Adequately capitalized Basel III phase-in schedule, amount |  | $ 1,326.2 | $ 1,379.7
Adequately capitalized Basel III phase-in schedule, ratio (percent) |  | 0.0600 | 0.0600
Adequately capitalized Basel III fully phased-in, amount |  | $ 1,878.8 | $ 1,954.6
Tier One Capital Required For Capital Adequacy Under Basel III Fully Phased-In To Risk Weighted Assets |  | 8.50% | 8.50%
Well capitalized, amount |  | $ 1,768.3 | $ 1,839.6
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets |  | 0.0800 | 0.0800
Common Equity Tier One Capital [Abstract] |  |  |
Actual amount |  | $ 2,433.0 | $ 2,504.1
Common Equity Tier One Risk Based Capital To Risk Weighted Assets |  | 11.01% | 10.89%
Adequately capitalized Basel III phase-in schedule, amount |  | $ 994.6 | $ 1,034.8
Adequately capitalized Basel III phase-in schedule, ratio (percent) |  | 4.50% | 4.50%
Adequately capitalized Basel III fully phased-in, amount |  | $ 1,547.2 | $ 1,609.7
Tier One Common Equity Capital Required For Capital Adequacy Under Basel III Fully Phased-In To Risk Weighted Assets |  | 7.00% | 7.00%
Well capitalized, amount |  | $ 1,436.7 | $ 1,494.7
Common Equity Tier One Capital To Be Well Capitalized To Risk Weighted Assets |  | 6.50% | 6.50%
Leverage capital ratio: |  |  |
Actual amount |  | $ 2,433.0 | $ 2,504.1
Tier One Leverage Capital to Average Assets |  | 0.0816 | 0.0807
Adequately capitalized, amount |  | $ 1,192.2 | $ 1,241.1
Adequately capitalized, ratio (percent) |  | 0.0400 | 0.0400
Well capitalized, amount |  | $ 1,490.2 | $ 1,551.4
Well capitalized, ratio (percent) |  | 0.0500 | 0.0500

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