Borrowings - FHLB and FRB Advances (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
FHLB advances	$ 0	$ 350,000,000
FRB PPP Liquidity Facility Advances	4,415,016,000	0
Total long-term FHLB and FRB advances	$ 4,415,016,000	$ 350,000,000
FHLB advances, interest rate	0.00%	2.36%
FRB PPP Liquidity Facility Advances, interest rate	0.35%	0.00%
Total maximum borrowing capacity with the FHLB	$ 2,729,516,000	$ 3,445,416,000
Total maximum borrowing capacity with the FRB	223,299,000	136,842,000
Qualifying loans serving as collateral against FHLB and FRB advances	3,363,364,000	$ 4,496,983,000
Credit Facility, CARES Act
Debt Instrument [Line Items]
FRB PPP liquidity facility	4,400,000,000
Maximum borrowing capacity	$ 4,700,000,000

CARES Act, Federal Reserve Bank, Interest Rate

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Federal reserve bank maximum amount available.

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Federal Reserve Bank, Payment Protection Program, Liquidity Facility Advances, CARES Act

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Amount of Federal Home Loan Bank (FHLBank) advances to member financial institutions.

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States the interest rate applicable to Federal Home Loan Bank advances outstanding as of the Balance Sheet date.

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Amount of maximum advances or credit lines available from the Federal Home Loan Bank (FHLB).

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The sum of the carrying amounts, as of the date of the latest financial statement presented, of loans receivable which are owned but transferred to serve as collateral for the payment of related debt obligations, primarily secured borrowings and repurchase agreements, and for which the transferees are not permitted to sell or re-pledge them to an unrelated party.

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