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Subsequent Event	6 Months Ended
Subsequent Event	Jun. 30, 2013
Subsequent Events [Abstract]
Subsequent Event	14. Subsequent Event In July 2013, the Corporation announced an agreement to sell its energy marketing business for $1,025 million before normal post-closing adjustments. The transaction is subject to regulatory approvals and other customary closing conditions and is expected to close in the fourth quarter of 2013.