Restricted Stock Awards and Restricted Stock Units Description of Performance Incentive Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Schedule of Restricted Stock Award and Restricted Stock Unit Activity [Line Items]
Vesting Period			4 years
Restricted Stock Units [Member]
Schedule of Restricted Stock Award and Restricted Stock Unit Activity [Line Items]
Share grants approved in period			1.6	0.9
Performance shares granted			0.7	0.4
Share Based Payment Expense for RSUs Expected to Vest	$ 2.2	$ 1.9	$ 8.1	$ 5.1
Restricted Stock Awards and Restricted Stock Units [Member]
Schedule of Restricted Stock Award and Restricted Stock Unit Activity [Line Items]
Vesting terms of RSUs and RSAs			Half of these performance incentive program grants vest ratably on each of the first three anniversaries of the grant date; 25% will vest upon achievement of certain performance metrics; and the remaining 25% will vest one year from the date upon which certain performance metrics are achieved. If actual performance metrics exceed the targeted performance metrics by a predetermined amount, the executives are eligible to receive up to 200% of the performance-based portion of their award.
Minimum [Member]
Schedule of Restricted Stock Award and Restricted Stock Unit Activity [Line Items]
Vesting Period			3 years
Maximum [Member]
Schedule of Restricted Stock Award and Restricted Stock Unit Activity [Line Items]
Vesting Period			4 years