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Regulatory Capital - Schedule of Actual Capital Amounts and Ratios and Selected Minimum Regulatory Thresholds (Details) - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Total risk-based capital: |  |
Actual Amount | $ 1,131.5 | $ 1,112.5
Actual Ratio | 12.90412% | 12.75962%
Capital Required for Capital Adequacy under Basel III Phase-in Schedule | $ 865.9 | $ 806.5
Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets | 9.875% | 9.25%
Capital Required for Capital Adequacy under Basel III Fully Phased-in | $ 920.7 | $ 915.5
Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets | 10.50% | 10.50%
Well Capitalized Amount | $ 876.8 | $ 871.9
Well Capitalized Ratio | 10.00% | 10.00%
Tier 1 risk-based capital: |  |
Actual Amount | $ 1,058.0 | $ 1,040.3
Actual Ratio | 12.06583% | 11.93154%
Tier One Risk Based Capital under Basel III Phase-in Schedule | $ 690.5 | $ 632.1
Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets | 7.875% | 7.25%
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in | $ 745.3 | $ 741.1
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets | 8.50% | 8.50%
Well Capitalized Amount | $ 701.5 | $ 697.5
Well Capitalized Ratio | 8.00% | 8.00%
Common equity tier one risk-based capital: |  |
Actual Amount | $ 978.0 | $ 962.4
Actual Ratio | 11.15347% | 11.03808%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule | $ 559.0 | $ 501.3
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets | 6.375% | 5.75%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in | $ 613.8 | $ 610.3
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets | 7.00% | 7.00%
Well Capitalized Amount | $ 569.9 | $ 566.7
Well Capitalized Ratio | 6.50% | 6.50%
Leverage capital ratio: |  |
Actual Amount | $ 1,058.0 | $ 1,040.3
Actual Ratio | 9.06934% | 8.85532%
Adequately Capitalized Amount | $ 466.6 | $ 469.9
Adequately Capitalized Ratio | 4.00% | 4.00%
Well Capitalized Amount | $ 583.3 | $ 587.4
Well Capitalized Ratio | 5.00% | 5.00%
FIB |  |
Total risk-based capital: |  |
Actual Amount | $ 1,070.5 | $ 1,066.6
Actual Ratio | 12.24921% | 12.29128%
Capital Required for Capital Adequacy under Basel III Phase-in Schedule | $ 863.0 | $ 802.7
Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets | 9.875% | 9.25%
Capital Required for Capital Adequacy under Basel III Fully Phased-in | $ 917.6 | $ 911.2
Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets | 10.50% | 10.50%
Well Capitalized Amount | $ 873.9 | $ 867.8
Well Capitalized Ratio | 10.00% | 10.00%
Tier 1 risk-based capital: |  |
Actual Amount | $ 997.0 | $ 994.4
Actual Ratio | 11.4081% | 11.45926%
Tier One Risk Based Capital under Basel III Phase-in Schedule | $ 688.2 | $ 629.1
Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets | 7.875% | 7.25%
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in | $ 742.8 | $ 737.6
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets | 8.50% | 8.50%
Well Capitalized Amount | $ 699.1 | $ 694.2
Well Capitalized Ratio | 8.00% | 8.00%
Common equity tier one risk-based capital: |  |
Actual Amount | $ 997.0 | $ 994.4
Actual Ratio | 11.4081% | 11.45926%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule | $ 557.1 | $ 499.0
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets | 6.375% | 5.75%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in | $ 611.7 | $ 607.4
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets | 7.00% | 7.00%
Well Capitalized Amount | $ 568.0 | $ 564.1
Well Capitalized Ratio | 6.50% | 6.50%
Leverage capital ratio: |  |
Actual Amount | $ 997.0 | $ 994.4
Actual Ratio | 8.54894% | 8.48004%
Adequately Capitalized Amount | $ 466.5 | $ 469.1
Adequately Capitalized Ratio | 4.00% | 4.00%
Well Capitalized Amount | $ 583.1 | $ 586.3
Well Capitalized Ratio | 5.00% | 5.00%

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- Definition The amount of total capital as defined in the regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 948 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47304-110998 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 948 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47080-110998 + Details
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- Definition The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826 + Details
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- Definition The minimum amount of Tier 1 Leverage Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826 + Details
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- Definition The amount of Tier 1 Leverage Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826 + Details
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