Basis of Presentation (Policies)	3 Months Ended
Mar. 31, 2012
Basis of Presentation [Abstract]
Fair Value Measurements	Effective January 1, 2012, the Corporation adopted FASB ASU 2011-04, Fair Value Measurement (Topic 820): Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRS. For the Corporation, this standard requires additional disclosures related to fair value measurements, which are included in Note 12, Risk Management and Trading Activities.
Comprehensive Income	Effective January 1, 2012, the Corporation adopted the provisions of Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) 2011-05, Comprehensive Income (Topic 220): Presentation of Comprehensive Income, which requires comprehensive income to be presented either at the end of the income statement or as a separate statement immediately following the income statement. The Corporation elected to adopt the separate statement method.

Basis of Presentation (Policies)

3 Months Ended

Mar. 31, 2012

Effective January 1, 2012, the Corporation adopted FASB ASU 2011-04, Fair Value Measurement (Topic 820): Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRS. For the Corporation, this standard requires additional disclosures related to fair value measurements, which are included in Note 12, Risk Management and Trading Activities.

Comprehensive Income

Effective January 1, 2012, the Corporation adopted the provisions of Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) 2011-05, Comprehensive Income (Topic 220): Presentation of Comprehensive Income, which requires comprehensive income to be presented either at the end of the income statement or as a separate statement immediately following the income statement. The Corporation elected to adopt the separate statement method.