Consolidated Statements Of Equity (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Common dividend per share	$ 1.16	$ 1.10	$ 1.04
6.75% Series D Preferred Shares [Member]
Preferred dividend per share	$ 50.63	$ 50.63	$ 50.63
6.95% Series E Preferred Shares [Member]
Preferred dividend per share	$ 162.16	$ 173.75	$ 173.75
6.5% Series F Preferred Shares [Member]
Preferred dividend per share	$ 162.50	$ 162.50	$ 162.50