Equity (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Equity [Abstract]
Net income	$ 96.9	$ 85.9	$ 268.6	$ 286.1
Average common shares outstanding	42.9	45.1	43.6	44.9
Incremental shares from restricted stock units, stock options and convertible debentures	0.6	0.9	0.9	0.7
Average diluted shares outstanding	43.5	46.0	44.5	45.6
Basic earnings per share (in dollars per share)	$ 2.26	$ 1.90	$ 6.16	$ 6.38
Diluted earnings per share (in dollars per share)	$ 2.23	$ 1.87	$ 6.03	$ 6.27
Shares outstanding	42.5	45.2	42.5	45.2
Anti-dilutive securities excluded from diluted earnings per share (in shares)	0	0.8	0	0.8
Dilutive effect of the debentures (in shares)	0.1	0	0.3	0