Outstanding and Weighted Average Common Shares (Tables)

12 Months Ended

Dec. 31, 2011

Outstanding and Weighted Average Common Shares [Abstract]

Changes in Corporation's outstanding common shares

	2011		2010		2009
	(Thousands of shares)
Balance at January 1		337,681		327,229		326,133
Issued for an acquisition*		—		8,602		—
Activity related to restricted common stock awards, net		579		770		680
Employee stock options		1,716		1,080		416
Balance at December 31		339,976		337,681		327,229

* See Note 2, Acquisitions and Dispositions in the notes to the Consolidated Financial Statements.

Weighted average number of common shares outstanding - basic and diluted

	2011		2010		2009
	(Thousands of shares)
Common shares — basic		336,901		325,999		323,890
Effect of dilutive securities
Stock options		1,617		829		836
Restricted common stock		1,380		1,449		1,239
Common shares — diluted		339,898		328,277		325,965