Share-based Compensation Awards (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock-settled awards
Stock-based Payment Award
Awards granted	0.9	0.8	3.7
Weighted-average grant-date fair value (per award)	$ 11.43	$ 11.94	$ 8.47
Total fair value of vested awards distributed	$ 63.5	$ 63.1	$ 36.4
Accrued dividends on non-vested stock-settled awards	1.1	2.5
Dividends paid for stock-settled awards	1.7	0.3
Cash-settled awards
Stock-based Payment Award
Awards granted	0.1	0	0.6
Weighted-average grant-date fair value (per award)	$ 10.94	$ 8.96	$ 8.50
Total fair value of vested awards distributed	11.1	10.4	4.8
Performance-based awards
Stock-based Payment Award
Awards granted	1.8	1.8	0.1
Weighted-average grant-date fair value (per award)	$ 10.61	$ 11.58	$ 11.02
Total fair value of vested awards distributed	$ 11.5	$ 30.8	$ 4.6