Investment Securities - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Held to maturity securities, assets pledged	$ 156,371,000,000	$ 159,452,000,000
Available for sale securities, assets pledged	101,086,000,000	107,646,000,000
Available for sale, written down to fair value	0	0
Writedown to fair value	0	0
Available for sale, allowance for credit loss	0	0
Held to maturity securities, allowance for credit loss	0	0
Accrued interest receivable	531,000,000	565,000,000
Write-off of accrued interest receivable on available for sale and held to maturity securities	0	0
Asset Pledged as Collateral
Debt Securities, Available-for-sale [Line Items]
Held to maturity securities, assets pledged	6,745,000,000	3,703,000,000
Available for sale securities, assets pledged	1,688,000,000	1,733,000,000
Asset Pledged as Collateral \| Interest rate swaps
Debt Securities, Available-for-sale [Line Items]
Available for sale securities, assets pledged	191,000,000	195,000,000
Federal Home Loan Bank Advances
Debt Securities, Available-for-sale [Line Items]
Value of securities held as collateral	68,200,000,000
Federal Reserve Bank Advances
Debt Securities, Available-for-sale [Line Items]
Value of securities held as collateral	32,900,000,000
Deposits
Debt Securities, Available-for-sale [Line Items]
Value of securities held as collateral	1,600,000,000
U.S. agency mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Held to maturity securities, assets pledged	156,371,000,000	159,452,000,000
Available for sale securities, assets pledged	60,171,000,000	$ 62,795,000,000
U.S. agency mortgage-backed securities \| Asset Pledged as Collateral \| Securities Sold under Agreements to Repurchase
Debt Securities, Available-for-sale [Line Items]
Held to maturity securities, assets pledged	6,700,000,000
Available for sale securities, assets pledged	$ 1,500,000,000

Debt Securities, Available-For-Sale And Held-To-Maturity, Accrued Interest, After Allowance For Credit Loss

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- Definition

Debt Securities, Available-For-Sale And Held-To-Maturity, Accrued Interest Writeoff

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Debt Securities, Available-for-Sale, Excluding Accrued Interest, Write-down To Fair Value

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Value of Securities Held as Collateral

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Amount excluding accrued interest, of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, excluding accrued interest, of decrease in allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) from writeoff.

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Amount, excluding accrued interest, of allowance for credit loss on investment in debt security measured at amortized cost (held-to-maturity).

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Amount excluding accrued interest, after allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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