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Regulatory Capital (Details) $ in Millions | Sep. 30, 2020 USD ($) | Jan. 01, 2020 USD ($) | Dec. 31, 2019 USD ($)
--- | --- | --- | ---
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |
Retained Earnings (Accumulated Deficit) | $ 938.9 |  | $ 953.6
Total risk-based capital: |  |  |
Actual, Amount | $ 1,585.8 |  | $ 1,495.3
Actual, Ratio | 0.1445 |  | 0.1410
Minimum Required for Capital Adequacy Purposes, Amount | $ 877.7 |  | $ 848.5
Minimum Required for Capital Adequacy Purposes, Ratio | 0.0800 |  | 0.0800
For Capital Adequacy Purposes Plus Capital Conservation Buffer, Amount | $ 1,152.0 |  | $ 1,113.6
For Capital Adequacy Purposes Plus Capital Conservation Buffer, Ratio | 10.50% |  | 10.50%
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Amount | $ 1,097.1 |  | $ 1,060.6
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Ratio | 0.1000 |  | 0.1000
Tier 1 risk-based capital: |  |  |
Actual, Amount | $ 1,378.3 |  | $ 1,422.3
Actual, Ratio | 0.1256 |  | 0.1341
Minimum Required for Capital Adequacy Purposes, Amount | $ 658.3 |  | $ 636.3
Minimum Required for Capital Adequacy Purposes, Ratio | 0.0600 |  | 0.0600
For Capital Adequacy Purposes Plus Capital Conservation Buffer, Amount | $ 932.6 |  | $ 901.5
For Capital Adequacy Purposes Plus Capital Conservation Buffer, Ratio | 8.50% |  | 8.50%
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Amount | $ 877.7 |  | $ 848.5
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Ratio | 0.0800 |  | 0.0800
Common equity tier 1 risk-based capital: |  |  |
Actual, Amount | $ 1,294.2 |  | $ 1,338.2
Actual, Ratio | 11.80% |  | 12.62%
Minimum Required for Capital Adequacy Purposes, Amount | $ 493.7 |  | $ 477.3
Minimum Required for Capital Adequacy Purposes, Ratio | 4.50% |  | 4.50%
For Capital Adequacy Purposes Plus Capital Conservation Buffer, Amount | $ 768.0 |  | $ 742.4
For Capital Adequacy Purposes Plus Capital Conservation Buffer, Ratio | 7.00% |  | 7.00%
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Amount | $ 713.1 |  | $ 689.4
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Ratio | 6.50% |  | 6.50%
Leverage capital ratio: |  |  |
Actual, Amount | $ 1,378.3 |  | $ 1,422.3
Actual, Ratio | 0.0862 |  | 0.1013
Banking Regulation, Tier One Leverage Capital, Capital Adequacy, Minimum | $ 639.3 |  | $ 561.6
Capital Adequacy Purposes and Conservation Buffer, Ratio | 0.0400 |  | 0.0400
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Amount | $ 799.1 |  | $ 702.0
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Ratio | 0.0500 |  | 0.0500
FIB |  |  |
Total risk-based capital: |  |  |
Actual, Amount | $ 1,412.5 |  | $ 1,321.4
Actual, Ratio | 0.1291 |  | 0.1250
Minimum Required for Capital Adequacy Purposes, Amount | $ 875.1 |  | $ 845.8
Minimum Required for Capital Adequacy Purposes, Ratio | 0.0800 |  | 0.0800
For Capital Adequacy Purposes Plus Capital Conservation Buffer, Amount | $ 1,148.6 |  | $ 1,110.1
For Capital Adequacy Purposes Plus Capital Conservation Buffer, Ratio | 10.50% |  | 10.50%
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Amount | $ 1,093.9 |  | $ 1,057.2
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Ratio | 0.1000 |  | 0.1000
Tier 1 risk-based capital: |  |  |
Actual, Amount | $ 1,305.1 |  | $ 1,248.4
Actual, Ratio | 0.1193 |  | 0.1181
Minimum Required for Capital Adequacy Purposes, Amount | $ 656.3 |  | $ 634.3
Minimum Required for Capital Adequacy Purposes, Ratio | 0.0600 |  | 0.0600
For Capital Adequacy Purposes Plus Capital Conservation Buffer, Amount | $ 929.8 |  | $ 898.6
For Capital Adequacy Purposes Plus Capital Conservation Buffer, Ratio | 8.50% |  | 8.50%
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Amount | $ 875.1 |  | $ 845.8
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Ratio | 0.0800 |  | 0.0800
Common equity tier 1 risk-based capital: |  |  |
Actual, Amount | $ 1,305.1 |  | $ 1,248.4
Actual, Ratio | 11.93% |  | 11.81%
Minimum Required for Capital Adequacy Purposes, Amount | $ 492.3 |  | $ 475.7
Minimum Required for Capital Adequacy Purposes, Ratio | 4.50% |  | 4.50%
For Capital Adequacy Purposes Plus Capital Conservation Buffer, Amount | $ 765.7 |  | $ 740.0
For Capital Adequacy Purposes Plus Capital Conservation Buffer, Ratio | 7.00% |  | 7.00%
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Amount | $ 711.0 |  | $ 687.2
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Ratio | 6.50% |  | 6.50%
Leverage capital ratio: |  |  |
Actual, Amount | $ 1,305.1 |  | $ 1,248.4
Actual, Ratio | 0.0818 |  | 0.0891
Banking Regulation, Tier One Leverage Capital, Capital Adequacy, Minimum | $ 638.2 |  | $ 560.4
Capital Adequacy Purposes and Conservation Buffer, Ratio | 0.0400 |  | 0.0400
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Amount | $ 797.8 |  | $ 700.4
Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements, Ratio | 0.0500 |  | 0.0500
Cumulative Effect, Period of Adoption, Adjustment |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |
Retained Earnings (Accumulated Deficit) |  | $ (24.1) |

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Name: | srt_CumulativeEffectPeriodOfAdoptionAxis=srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |