Consolidated Statements of Changes in Equity (Parenthetical) (USD $)	3 Months Ended												12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2009
Common stock dividends declared (in dollars per share)	$ 0.325	[1]	$ 0.320	[1]	$ 0.320	[1]	$ 0.320	[1]	$ 0.320	$ 0.315	$ 0.315	$ 0.315	$ 1.285	[1]	$ 1.265	$ 1.245

[1] Due to a loss for the three months and year ended December 31, 2011, there are no incremental shares in the diluted computation because such shares would be considered antidilutive.