Earnings Per Common Share (Computation Of Basic And Diluted Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Earnings Per Share [Abstract]
Net income allocated to common shares	$ 96	$ 146	$ 335	$ 390
Weighted average number of common shares outstanding - basic (in shares)	237,838	208,545	218,694	208,435
Effect of potentially dilutive common shares (in shares)	1,087	909	1,018	702
Weighted average number of shares outstanding, diluted (in shares)	238,925	209,454	219,712	209,137
Earnings per common share:
Basic (in dollars per share)	$ 0.40	$ 0.70	$ 1.53	$ 1.87
Diluted (in dollars per share)	$ 0.40	$ 0.70	$ 1.53	$ 1.87

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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+ Details

- Definition

Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

+ References

+ Details

COLUMBIA BANKING SYSTEM, INC. 10-Q