Condensed Consolidated Statements Of Equity (Parenthetical) (USD $)	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Common dividend per share	$ 0.870	$ 0.825
6.75% Series D Preferred Shares [Member]
Preferred dividend per share	$ 37.97	$ 37.97
6.95% Series E Preferred Shares [Member]
Preferred dividend per share	$ 130.31	$ 130.31
6.5% Series F Preferred Shares [Member]
Preferred dividend per share	$ 121.88	$ 121.88