v3.25.3

Debt Securities (Amortized Cost, Unrealized Gains And Losses, And Fair Value Of Investment Securities) (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Debt and Equity Securities, FV-NI [Line Items]
Available-for-sale securities, amortized cost	$ 11,334	$ 8,858
Available-for-sale securities, unrealized gains	89	8
Available-for-sale securities, unrealized losses	(410)	(591)
Available for sale, at fair value	11,013	8,275
Investment securities held to maturity	18	2
Held-to-maturity securities, unrealized gains	0	1
Held-to-maturity securities, unrealized losses	0	0
Held-to-maturity securities, fair value	18	3
U.S. Treasury and agencies
Debt and Equity Securities, FV-NI [Line Items]
Available-for-sale securities, amortized cost	1,332	1,496
Available-for-sale securities, unrealized gains	6	1
Available-for-sale securities, unrealized losses	(43)	(74)
Available for sale, at fair value	1,295	1,423
Obligations of states and political subdivisions
Debt and Equity Securities, FV-NI [Line Items]
Available-for-sale securities, amortized cost	1,621	1,055
Available-for-sale securities, unrealized gains	34	3
Available-for-sale securities, unrealized losses	(18)	(32)
Available for sale, at fair value	1,637	1,026
Mortgage-backed securities and collateralized mortgage obligations
Debt and Equity Securities, FV-NI [Line Items]
Available-for-sale securities, amortized cost	8,381	6,307
Available-for-sale securities, unrealized gains	49	4
Available-for-sale securities, unrealized losses	(349)	(485)
Available for sale, at fair value	8,081	5,826
Investment securities held to maturity	18	2
Held-to-maturity securities, unrealized gains	0	1
Held-to-maturity securities, unrealized losses	0	0
Held-to-maturity securities, fair value	$ 18	$ 3

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) 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, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

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COLUMBIA BANKING SYSTEM, INC. 10-Q