Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Class of Stock [Line Items]
Common shares, par value	$ 0.10	$ 0.10
Common shares, shares authorized	500,000,000	500,000,000
Common shares, shares issued	277,558,873	277,114,784
Common shares in treasury at cost	705,953	833,934
Class H Preferred Shares
Class of Stock [Line Items]
Cumulative redeemable preferred shares, par value
Cumulative redeemable preferred shares, liquidation value	$ 500	$ 500
Cumulative redeemable preferred shares, shares authorized	750,000	750,000
Cumulative redeemable preferred shares, shares issued	410,000	410,000
Cumulative redeemable preferred shares, shares outstanding	410,000	410,000
Preferred stock dividend rate	7.375%	7.375%
Class I Preferred Shares
Class of Stock [Line Items]
Cumulative redeemable preferred shares, par value
Cumulative redeemable preferred shares, liquidation value	$ 500	$ 500
Cumulative redeemable preferred shares, shares authorized	750,000	750,000
Cumulative redeemable preferred shares, shares issued	340,000	340,000
Cumulative redeemable preferred shares, shares outstanding	340,000	340,000
Preferred stock dividend rate	7.50%	7.50%