Share-based Compensation Awards (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stock-settled awards
Stock-based Payment Award
Awards granted	0.8	3.7	7.8
Weighted-average grant-date fair value (per award)	$ 11.94	$ 8.47	$ 4.21
Total fair value of vested awards distributed	$ 63.1	$ 36.4	$ 23.8
Accrued dividends on non-vested stock-settled awards	2.5
Dividends paid for stock-settled awards	0.3
Cash-settled awards
Stock-based Payment Award
Awards granted	0	0.6	1.4
Weighted-average grant-date fair value (per award)	$ 8.96	$ 8.50	$ 4.43
Total fair value of vested awards distributed	10.4	4.8	7.5
Performance-based awards
Stock-based Payment Award
Awards granted	1.8	0.1	1.7
Weighted-average grant-date fair value (per award)	$ 11.58	$ 11.02	$ 6.25
Total fair value of vested awards distributed	$ 30.8	$ 4.6	$ 29.4