Accumulated Other Comprehensive Income (Schedule Of Accumulated Other Comprehensive Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Dec. 31, 2010
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Unrealized Gains (Losses) on Securities, OTTI, Balance	$ 3,271	$ (4,634)	$ 3,271	$ (4,634)	$ (4,321)	$ (7,469)
Unrealized Gains (Losses) on Securities, OTTI, Current period other comprehensive income (loss)	3,695	(676)	7,592	2,835
Unrealized Gains (Losses) on Securities, Other, Balance	182,689	136,206	182,689	136,206	136,137	87,784
Unrealized Gains (Losses) on Securities, Other, Current period other comprehensive income (loss)	25,160	32,948	46,552	48,422
Pension Loss, Balance	(19,920)	(15,791)	(19,920)	(15,791)	(21,278)	(16,970)
Pension Loss, Current period other comprehensive income			1,358	1,179
Total Accumulated Other Comprehensive Income, Balance	166,040	115,781	166,040	115,781	110,538	63,345
Comprehensive income attributable to Commerce Bancshares, Inc	$ 29,308	$ 32,781	$ 55,502	$ 52,436

The total of net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost.

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+ Details

- Definition

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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+ Details

- Definition

This element represents Other Comprehensive Income or Loss, Net of Tax, for the period. Includes deferred gains or losses on qualifying hedges, unrealized holding gains or losses on available-for-sale securities, minimum pension liability, and cumulative translation adjustment. While for technical reasons this element has no balance attribute, the default assumption is a credit balance consistent with its label.

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+ Details