Shareholders' Equity (Tables)

12 Months Ended

Dec. 31, 2011

Disclosure - Shareholders Equity [Abstract]

Total Authorized Shares Table [Text Block]

	2011	2010
Designated common shares	130.0	130.0
Designated 6.75% Series C cumulative redeemable preferred shares	11.6	11.6
Designated 6.5% Series D cumulative redeemable preferred shares	9.2	9.2
Designated 7.25% Series E cumulative redeemable preferred shares	15.0	—
Designated and redeemed preference shares	14.0	14.0
Undesignated	20.2	35.2
	200.0	200.0

Preferred Stock [Table Text Block]

	Series C			Series D			Series E
Date of issuance		May 2003			November 2004			June 2011
Number of preferred shares issued		11.6			9.2			15.0
Annual dividend rate		6.75	%		6.5	%		7.25	%
Total consideration	$	280.9		$	222.3		$	361.7
Underwriting discounts and commissions	$	9.1		$	7.7		$	12.1
Aggregate liquidation value	$	290.0		$	230.0		$	373.8