Commitments, Contingencies and Guarantees - Narrative (Details)		1 Months Ended		9 Months Ended
	Jun. 27, 2018 USD ($)	Apr. 30, 2020 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2020 USD ($) claim	Dec. 31, 2019 USD ($)	Apr. 30, 2018 claim	Jan. 31, 2017 claim
Loss Contingencies [Line Items]
Loss contingency accrual				$ 25,000,000
Number of claims pending | claim				2
Minimum
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss				$ 0
Maximum
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss				76,000,000
Financial Standby Letter of Credit
Loss Contingencies [Line Items]
Letters of credit, deferred fees				7,000,000	$ 7,000,000
Maximum potential amount of future undiscounted payments Company could be required to make on outstanding standby letters of credit				$ 923,000,000
Financial Standby Letter of Credit | Minimum
Loss Contingencies [Line Items]
Standby and commercial letters of credit expiration term				1 year
Financial Standby Letter of Credit | Maximum
Loss Contingencies [Line Items]
Standby and commercial letters of credit expiration term				4 years
Potential Recourse Related to FNMA Securitizations | Maximum
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss				$ 18,000,000	18,000,000
Accrued Expenses and Other Liabilities | Financial Standby Letter of Credit
Loss Contingencies [Line Items]
Loss contingency accrual				144,000,000	67,000,000
Accrued Expenses and Other Liabilities | Potential Recourse Related to FNMA Securitizations
Loss Contingencies [Line Items]
Loss contingency accrual				693,000	693,000
Accrued Expenses and Other Liabilities | Standard Representations and Warranties Related to Loan Sales to Government-Sponsored Agencies
Loss Contingencies [Line Items]
Loss contingency accrual				$ 3,000,000	$ 1,200,000
Pending Litigation | David Lannon Powell Finneran v. BBVA USA Bancshares, Inc., et al.
Loss Contingencies [Line Items]
Number of claims pending | claim							1
Pending Litigation | David L. Powell, et al. v. BBVA USA
Loss Contingencies [Line Items]
Number of claims pending | claim						1
Pending Litigation | Minimum | Zamora-Orduna Realty Group LLC v. BBVA USA
Loss Contingencies [Line Items]
Damages sought, value		$ 10,000,000
Settled Litigation | David S. Bagwell Trust, et al. v. BBVA USA, et al.
Loss Contingencies [Line Items]
Amount awarded to other party			$ 98,000,000
Damages awarded, value	$ 96,000,000