Share-Based Compensation Arrangements (Policies)	12 Months Ended
Share-Based Compensation Arrangements (Policies)	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation plans provide for awards of share options and other equity incentives including nonvested share units and share awards and nonvested performance shares. Compensation expense for share options and nonvested share units and share awards is recognized over the service period based on the fair value at the date of grant. The Corporation estimates grant date fair value for share options using the Black-Scholes option-pricing model. Nonvested performance share compensation expense is based on the most recent performance assumption available and is adjusted as assumptions change. Excess tax benefits (expenses) related to stock option exercises and issuance of other compensation-related equity instruments are reflected on the Consolidated Statements of Cash Flows as financing activity. Compensation expense for share options, nonvested shares and nonvested share units is recognized over the service period based on the fair value at the date of grant. Nonvested performance share compensation expense is based on the most recent performance assumption available and is adjusted as assumptions change. If the goals are not met, no compensation cost will be recognized and any recognized compensation costs will be reversed.

Disclosure of accounting policy for stock option and stock incentive plans. This disclosure may include (1) the types of stock option or incentive plans sponsored by the entity (2) the groups that participate in (or are covered by) each plan (3) significant plan provisions and (4) how stock compensation is measured, and the methodologies and significant assumptions used to determine that measurement.

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