Regulatory matters - Additional Information (Detail) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Funds available for payment of dividends to M&T from banking subsidiaries	$ 944,000,000
Required subsidiary noninterest-earning reserves against certain deposit liabilities	604,789,000	382,489,000
Minimum "Tier 1 capital" ratio required for capital adequacy	4.00%
Minimum "Total capital" ratio required for capital adequacy	8.00%
Minimum "Leverage" ratio required for capital adequacy	3.00%
Minimum "Tier 1" capital" ratio to be considered well capitalized	6.00%
Minimum "Total capital" ratio to be considered well capitalized	10.00%
Minimum "Leverage" ratio to be considered well capitalized	5.00%
Minimum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Consolidated assets required per Federal Reserve Board to submit annual capital plans	$ 50,000,000,000

Assets Required To Submit Annual Capital Plans Per Federal Reserve Board

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Average daily balance of required Noninterest reserves against certain deposits.

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Funds available for payment of dividends to parent company from banking subsidiaries.

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- Definition

The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

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The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

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The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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