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Accumulated Other Comprehensive (Loss) Income - Schedule of Pretax and After-tax Components of Other Comprehensive Income (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2023 | Mar. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
AOCI activity before reclassification, net amount | $ 53.0 | $ (318.0)
Amounts reclassified from AOCI | 13.0 | 3.0
Gross Unrealized | 88.0 | (415.0)
Income Taxes | (22.0) | 100.0
Other comprehensive income (loss), net of tax | 66.0 | (315.0)
Net realized losses on sales of investment securities available for sale | 14.0 | 0.0
Investment securities available for sale, allowance for credit loss | 4.0 |
Defined benefit pension items |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
AOCI activity before reclassification, gross amount | 10.0 | 0.0
AOCI activity before reclassification, tax | (2.0) | 0.0
AOCI activity before reclassification, net amount | 8.0 | 0.0
Amounts reclassified from AOCI | 0.0 | 2.0
Gross Unrealized | 10.0 | 3.0
Income Taxes | (2.0) | (1.0)
Other comprehensive income (loss), net of tax | 8.0 | 2.0
Defined benefit pension items | Other noninterest expense |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Reclassification out of AOCI, gross amount | 0.0 | 3.0
Reclassification out of AOCI, tax | 0.0 | (1.0)
Amounts reclassified from AOCI | 0.0 | 2.0
Unrealized loss on securities available for sale |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
AOCI activity before reclassification, gross amount | 60.0 | (419.0)
AOCI activity before reclassification, tax | (15.0) | 101.0
AOCI activity before reclassification, net amount | 45.0 | (318.0)
Gross Unrealized | 78.0 | (419.0)
Income Taxes | (20.0) | 101.0
Other comprehensive income (loss), net of tax | 58.0 | (318.0)
Unrealized loss on securities available for sale | $14 realized loss on sales of investment securities available for sale, net; $4 provision for credit losses |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Reclassification out of AOCI, gross amount | 18.0 | 0.0
Reclassification out of AOCI, tax | (5.0) | 0.0
Amounts reclassified from AOCI | 13.0 | 0.0
Unrealized loss on securities available for sale transferred to securities held to maturity |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
AOCI activity before reclassification, gross amount | 0.0 | 0.0
AOCI activity before reclassification, tax | 0.0 | 0.0
AOCI activity before reclassification, net amount | 0.0 | 0.0
Amounts reclassified from AOCI | 0.0 | 1.0
Gross Unrealized | 0.0 | 1.0
Income Taxes | 0.0 | 0.0
Other comprehensive income (loss), net of tax | 0.0 | 1.0
Unrealized loss on securities available for sale transferred to securities held to maturity | Interest on investment securities |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Reclassification out of AOCI, gross amount | 0.0 | 1.0
Reclassification out of AOCI, tax | 0.0 | 0.0
Amounts reclassified from AOCI | 0.0 | 1.0
Unrealized (loss) gain on securities available for sale |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
AOCI activity before reclassification, net amount | 45.0 | (318.0)
Amounts reclassified from AOCI | 13.0 | 0.0
Other comprehensive income (loss), net of tax | $ 58.0 | $ (318.0)

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