Basis of Presentation	3 Months Ended
Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation General The accounting and reporting policies of the Company and the methods of applying those policies that materially affect the consolidated financial statements conform with U.S. GAAP and with general financial services industry practices. The accompanying unaudited consolidated financial statements include the accounts of BBVA Compass Bancshares, Inc. and its subsidiaries and have been prepared in conformity with U.S. GAAP for interim financial information and in accordance with the instructions to Quarterly Report on Form 10-Q and Article 10 of Regulation S-X as promulgated by the Securities and Exchange Commission. In the opinion of management, all adjustments, consisting of normal and recurring items, necessary for the fair presentation of the condensed consolidated financial statements have been included. Operating results for the three months ended March 31, 2018, are not necessarily indicative of the results that may be expected for the year ended December 31, 2018. These interim financial statements should be read in conjunction with the consolidated financial statements and notes thereto in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017. The Company has evaluated subsequent events for potential recognition and disclosure through the filing date of this Quarterly Report on Form 10-Q to determine if either recognition or disclosure of significant events or transactions is required. Use of Estimates in the Preparation of Consolidated Financial Statements The preparation of consolidated financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period, the most significant of which relate to the allowance for loan losses, goodwill impairment, fair value measurements and income taxes. Actual results could differ from those estimates. Recently Adopted Accounting Standards Revenue from Contracts with Customers In May 2014, the FASB released ASU 2014-09, Revenue from Contracts with Customers. The core principle of this codified guidance requires an entity to recognize revenue upon the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Because the guidance does not apply to revenue associated with financial instruments, including loans and securities accounted for under other U.S. GAAP, the new revenue recognition guidance did not have a material impact on the elements of the Company's statement of income most closely associated with financial instruments, including securities gains, interest income and interest expense. On January 1, 2018, the Company adopted the amendments to the revenue recognition principles utilizing a modified retrospective transition method applied to all contracts with customers outstanding upon adoption. Results for reporting periods beginning after January 1, 2018, are presented in accordance with the amendments to the revenue recognition principles, while prior period amounts have not been adjusted and continue to be presented in accordance with our historical accounting policies. The Company's implementation efforts include the identification of revenue within the scope of the guidance, as well as the evaluation of revenue contracts. The implementation of amendments to the revenue recognition standard had no impact on the measurement or recognition of revenue of prior periods. The Company did identify a prospective change in presentation of underwriting revenue and expenses, which will be shown gross in investment banking and advisory fees and other noninterest expense pursuant to the new requirements. The net quantitative impact of this presentation change to noninterest income and noninterest expense is immaterial and did not affect net income. See Note 12, Revenue from Contracts with Customers, for the required quantitative and qualitative disclosures in accordance with this ASU. Recognition and Measurement of Financial Assets and Liabilities In January 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Liabilities. The amendments in this ASU revise an entity's accounting related to the classification and measurement of investments in equity securities and the presentation of certain fair value changes for financial liabilities measured at fair value. The ASU also amends certain disclosure requirements associated with the fair value of financial instruments. On January 1, 2018, the Company adopted the amendments in this ASU. Effective as of January 1, 2018, all equity securities previously classified as AFS securities were reclassified to other assets as the AFS classification is no longer permitted for equity securities under this ASU. This reclassification has been made for all periods presented. Additionally, an immaterial adjustment from accumulated other comprehensive income (loss) to accumulated deficit was made related to the unrealized gains associated with these equity securities. The remaining provisions of this ASU did not have a material impact on the Company's Consolidated Financial Statements and related disclosures upon adoption. Included in the equity securities that were reclassified from AFS securities to other assets at January 1, 2018, was $450 million of FHLB and Federal Reserve stock carried at par that was not accounted for under ASC Topic 320 but had historically been presented in AFS securities. This reclassification has been made for all periods presented. This reclassification was immaterial and had no effect on net income, comprehensive income, total assets, or total shareholder's equity as previously reported. Statement of Cash Flows In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows - Classification of Certain Cash Receipts and Cash Payments, which provides guidance on eight specific cash flow issues with the objective of reducing the existing diversity in practice. Effective as of January 1, 2018, the adoption date, the Company changed the presentation of certain cash payments and receipts within its Condensed Consolidated Statements of Cash Flows. These changes were applied retrospectively to all periods presented within the statement of cash flows. For the three months ended March 31, 2017, the Company reclassified an immaterial amount of proceeds from the settlement of bank-owned life insurance policies and premiums paid for bank owned life insurance policies from operating activities to investing activities. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows - Restricted Cash. The amendments in this ASU require that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. The Company adopted this ASU on January 1, 2018. The amendments in this were ASU were applied retrospectively to all periods presented within the statement of cash flows. The implementation of this guidance resulted in a change in presentation of the Company's Condensed Consolidated Statement of Cash Flows and additional disclosures surrounding restricted cash balances. See Note 10, Supplemental Disclosure for Statement of Cash Flows, for the required disclosures in accordance with this ASU. Retirement Benefits In March 2017, the FASB issued ASU 2017-07, Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. The amendments in this ASU require that an employer disaggregate the service cost component from the other components of net benefit cost. The amendments also provide explicit guidance on how to present the service cost component and the other components of net benefit cost in the income statement and allow only the service cost component of net benefit cost to be eligible for capitalization. The Company adopted this ASU on January 1, 2018. The adoption of this standard did not have a material impact on the financial condition or results of operations of the Company. Income Taxes In March 2018, the FASB issued ASU 2018-05, Income Taxes (Topic 740): Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118. The amendments in this ASU codified into existing U.S. GAAP the SEC Staff views expressed in Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act which allows companies to record provisional amounts during a measurement period not to extend beyond one year of the enactment date. Since the Tax Cuts and Jobs Act was enacted late in 2017, the Company expects ongoing guidance, analysis, and accounting interpretations, including additional information about facts and circumstances that existed at the enactment date when the Company files its federal tax return for the tax year 2018, which could result in adjustments to the Tax Cuts and Jobs Act accounting effects recorded during 2017. The Company expects to complete its analysis within the measurement period in accordance with this ASU. Recently Issued Accounting Standards Not Yet Adopted Leases In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). The FASB issued this ASU to increase transparency and comparability among organizations by requiring lessees to present lease assets and lease liabilities on the balance sheet for those leases classified as operating leases under current U.S. GAAP and by disclosing key information about leasing arrangements. The amendments in this ASU are effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2018. Early application of this ASU is permitted for all entities. The Company is currently assessing the impact that the adoption of this standard will have on the financial condition and results of operations of the Company. Credit Losses In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses, which introduces new guidance for the accounting for credit losses on instruments within its scope. The new guidance introduces an approach based on expected losses to estimate credit losses on certain types of financial instruments. It also modifies the impairment model for AFS debt securities and provides for a simplified accounting model for purchased financial assets with credit deterioration since their origination. The amendments in this ASU are effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2019. Early application of this ASU is permitted. The Company is currently assessing the impact that the adoption of this standard will have on the financial condition and results of operations of the Company. Goodwill In January 2017, the FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment, which simplifies the manner in which an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Under the amendments in this ASU, an entity should (1) perform its annual or interim goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount, and (2) recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value, with the understanding that the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. Additionally, ASU No. 2017-04 removes the requirements for any reporting unit with a zero or negative carrying amount to perform a qualitative assessment and, if it fails such qualitative test, to perform Step 2 of the goodwill impairment test. This ASU is effective for fiscal years beginning after December 15, 2019, and for interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. The ASU should be applied using a prospective method. The Company is currently assessing this ASU and the impact of adoption. Premium Amortization on Purchased Callable Debt Securities In March 2017, the FASB issued ASU 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20), Premium Amortization on Purchased Callable Debt Securities. The amendments in this ASU reduce the amortization period for certain callable debt securities carried at a premium and require the premium to be amortized over a period not to exceed the earliest call date. These amendments do not apply to securities carried at a discount. This ASU is effective for fiscal years beginning after December 15, 2018, and for interim periods within those fiscal years. Early adoption is permitted. The ASU should be applied using a modified retrospective method. The adoption of this standard is not expected to have a material impact on the financial condition or results of operations of the Company. Derivatives and Hedging In August 2017, the FASB issued ASU 2017-12, Derivatives and Hedging (Topic 815), Targeted Improvements to Accounting for Hedging Activities. The amendments in this ASU better align an entity's risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. This ASU is effective for fiscal years beginning after December 15, 2018, and for interim periods within those fiscal years. Early adoption is permitted. The Company is currently assessing this ASU and the impact of adoption. Comprehensive Income In February 2018, the FASB issued ASU 2018-02, Income Statement - Reporting Comprehensive Income, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. The amendments in this ASU allow a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. This ASU is effective for fiscal years beginning after December 15, 2018, and for interim periods within those fiscal years. Early adoption is permitted. The Company is currently assessing this ASU and the impact of adoption.

Basis of Presentation

General

The accounting and reporting policies of the Company and the methods of applying those policies that materially affect the consolidated financial statements conform with U.S. GAAP and with general financial services industry practices. The accompanying unaudited consolidated financial statements include the accounts of BBVA Compass Bancshares, Inc. and its subsidiaries and have been prepared in conformity with U.S. GAAP for interim financial information and in accordance with the instructions to Quarterly Report on Form 10-Q and Article 10 of Regulation S-X as promulgated by the Securities and Exchange Commission. In the opinion of management, all adjustments, consisting of normal and recurring items, necessary for the fair presentation of the condensed consolidated financial statements have been included. Operating results for the three months ended March 31, 2018, are not necessarily indicative of the results that may be expected for the year ended December 31, 2018. These interim financial statements should be read in conjunction with the consolidated financial statements and notes thereto in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017.

The Company has evaluated subsequent events for potential recognition and disclosure through the filing date of this Quarterly Report on Form 10-Q to determine if either recognition or disclosure of significant events or transactions is required.

Use of Estimates in the Preparation of Consolidated Financial Statements

The preparation of consolidated financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period, the most significant of which relate to the allowance for loan losses, goodwill impairment, fair value measurements and income taxes. Actual results could differ from those estimates.

Recently Adopted Accounting Standards

Revenue from Contracts with Customers

In May 2014, the FASB released ASU 2014-09, Revenue from Contracts with Customers. The core principle of this codified guidance requires an entity to recognize revenue upon the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Because the guidance does not apply to revenue associated with financial instruments, including loans and securities accounted for under other U.S. GAAP, the new revenue recognition guidance did not have a material impact on the elements of the Company's statement of income most closely associated with financial instruments, including securities gains, interest income and interest expense.

On January 1, 2018, the Company adopted the amendments to the revenue recognition principles utilizing a modified retrospective transition method applied to all contracts with customers outstanding upon adoption. Results for reporting periods beginning after January 1, 2018, are presented in accordance with the amendments to the revenue recognition principles, while prior period amounts have not been adjusted and continue to be presented in accordance with our historical accounting policies. The Company's implementation efforts include the identification of revenue within the scope of the guidance, as well as the evaluation of revenue contracts. The implementation of amendments to the revenue recognition standard had no impact on the measurement or recognition of revenue of prior periods. The Company did identify a prospective change in presentation of underwriting revenue and expenses, which will be shown gross in investment banking and advisory fees and other noninterest expense pursuant to the new requirements. The net quantitative impact of this presentation change to noninterest income and noninterest expense is immaterial and did not affect net income.

See Note 12, Revenue from Contracts with Customers, for the required quantitative and qualitative disclosures in accordance with this ASU.

Recognition and Measurement of Financial Assets and Liabilities

In January 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Liabilities. The amendments in this ASU revise an entity's accounting related to the classification and measurement of investments in equity securities and the presentation of certain fair value changes for financial liabilities measured at fair value. The ASU also amends certain disclosure requirements associated with the fair value of financial instruments. On January 1, 2018, the Company adopted the amendments in this ASU. Effective as of January 1, 2018, all equity securities previously classified as AFS securities were reclassified to other assets as the AFS classification is no longer permitted for equity securities under this ASU. This reclassification has been made for all periods presented. Additionally, an immaterial adjustment from accumulated other comprehensive income (loss) to accumulated deficit was made related to the unrealized gains associated with these equity securities. The remaining provisions of this ASU did not have a material impact on the Company's Consolidated Financial Statements and related disclosures upon adoption.

Included in the equity securities that were reclassified from AFS securities to other assets at January 1, 2018, was $450 million of FHLB and Federal Reserve stock carried at par that was not accounted for under ASC Topic 320 but had historically been presented in AFS securities. This reclassification has been made for all periods presented. This reclassification was immaterial and had no effect on net income, comprehensive income, total assets, or total shareholder's equity as previously reported.

Statement of Cash Flows

In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows - Classification of Certain Cash Receipts and Cash Payments, which provides guidance on eight specific cash flow issues with the objective of reducing the existing diversity in practice. Effective as of January 1, 2018, the adoption date, the Company changed the presentation of certain cash payments and receipts within its Condensed Consolidated Statements of Cash Flows. These changes were applied retrospectively to all periods presented within the statement of cash flows. For the three months ended March 31, 2017, the Company reclassified an immaterial amount of proceeds from the settlement of bank-owned life insurance policies and premiums paid for bank owned life insurance policies from operating activities to investing activities.

In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows - Restricted Cash. The amendments in this ASU require that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. The Company adopted this ASU on January 1, 2018. The amendments in this were ASU were applied retrospectively to all periods presented within the statement of cash flows. The implementation of this guidance resulted in a change in presentation of the Company's Condensed Consolidated Statement of Cash Flows and additional disclosures surrounding restricted cash balances. See Note 10, Supplemental Disclosure for Statement of Cash Flows, for the required disclosures in accordance with this ASU.

Retirement Benefits

In March 2017, the FASB issued ASU 2017-07, Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. The amendments in this ASU require that an employer disaggregate the service cost component from the other components of net benefit cost. The amendments also provide explicit guidance on how to present the service cost component and the other components of net benefit cost in the income statement and allow only the service cost component of net benefit cost to be eligible for capitalization. The Company adopted this ASU on January 1, 2018. The adoption of this standard did not have a material impact on the financial condition or results of operations of the Company.

Income Taxes

In March 2018, the FASB issued ASU 2018-05, Income Taxes (Topic 740): Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118. The amendments in this ASU codified into existing U.S. GAAP the SEC Staff views expressed in Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act which allows companies to record provisional amounts during a measurement period not to extend beyond one year of the enactment date. Since the Tax Cuts and Jobs Act was enacted late in 2017, the Company expects ongoing guidance, analysis, and accounting interpretations, including additional information about facts and circumstances that existed at the enactment date when the Company files its federal tax return for the tax year 2018, which could result in adjustments to the Tax Cuts and Jobs Act accounting effects recorded during 2017. The Company expects to complete its analysis within the measurement period in accordance with this ASU.

Recently Issued Accounting Standards Not Yet Adopted

Leases

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). The FASB issued this ASU to increase transparency and comparability among organizations by requiring lessees to present lease assets and lease liabilities on the balance sheet for those leases classified as operating leases under current U.S. GAAP and by disclosing key information about leasing arrangements. The amendments in this ASU are effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2018. Early application of this ASU is permitted for all entities. The Company is currently assessing the impact that the adoption of this standard will have on the financial condition and results of operations of the Company.

Credit Losses

In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses, which introduces new guidance for the accounting for credit losses on instruments within its scope. The new guidance introduces an approach based on expected losses to estimate credit losses on certain types of financial instruments. It also modifies the impairment model for AFS debt securities and provides for a simplified accounting model for purchased financial assets with credit deterioration since their origination. The amendments in this ASU are effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2019. Early application of this ASU is permitted. The Company is currently assessing the impact that the adoption of this standard will have on the financial condition and results of operations of the Company.

Goodwill

In January 2017, the FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment, which simplifies the manner in which an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Under the amendments in this ASU, an entity should (1) perform its annual or interim goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount, and (2) recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value, with the understanding that the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. Additionally, ASU No. 2017-04 removes the requirements for any reporting unit with a zero or negative carrying amount to perform a qualitative assessment and, if it fails such qualitative test, to perform Step 2 of the goodwill impairment test. This ASU is effective for fiscal years beginning after December 15, 2019, and for interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. The ASU should be applied using a prospective method. The Company is currently assessing this ASU and the impact of adoption.

Premium Amortization on Purchased Callable Debt Securities

In March 2017, the FASB issued ASU 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20), Premium Amortization on Purchased Callable Debt Securities. The amendments in this ASU reduce the amortization period for certain callable debt securities carried at a premium and require the premium to be amortized over a period not to exceed the earliest call date. These amendments do not apply to securities carried at a discount. This ASU is effective for fiscal years beginning after December 15, 2018, and for interim periods within those fiscal years. Early adoption is permitted. The ASU should be applied using a modified retrospective method. The adoption of this standard is not expected to have a material impact on the financial condition or results of operations of the Company.

Derivatives and Hedging

In August 2017, the FASB issued ASU 2017-12, Derivatives and Hedging (Topic 815), Targeted Improvements to Accounting for Hedging Activities. The amendments in this ASU better align an entity's risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. This ASU is effective for fiscal years beginning after December 15, 2018, and for interim periods within those fiscal years. Early adoption is permitted. The Company is currently assessing this ASU and the impact of adoption.

Comprehensive Income

In February 2018, the FASB issued ASU 2018-02, Income Statement - Reporting Comprehensive Income, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. The amendments in this ASU allow a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. This ASU is effective for fiscal years beginning after December 15, 2018, and for interim periods within those fiscal years. Early adoption is permitted. The Company is currently assessing this ASU and the impact of adoption.