Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net income	$ 44.6	$ 67.4	$ 73.9	$ 19.9	$ 35.2	$ 64.3	$ 64.3	$ 8.0	$ 205.8	$ 171.8	$ 90.0
Net loss from discontinued operations									2.3	8.1	45.0
Income from continuing operations									$ 208.1	$ 179.9	$ 135.0
Weighted-average shares outstanding - basic									47.9	49.8	50.7
Effect of diluted securities attributable to stock-based payments									0.7	0.8	0.7
Weighted-average shares outstanding - diluted									48.6	50.6	51.4
Earnings per share – Basic:
Income from continuing operations									$ 4.35	$ 3.61	$ 2.66
Loss from discontinued operations									$ (0.05)	$ (0.16)	$ (0.89)
Net income	$ 0.98	$ 1.40	$ 1.51	$ 0.41	$ 0.72	$ 1.29	$ 1.28	$ 0.16	$ 4.30	$ 3.45	$ 1.77
Earnings per share – Diluted:
Income from continuing operations									$ 4.28	$ 3.55	$ 2.63
Loss from discontinued operations									$ (0.05)	$ (0.16)	$ (0.88)
Net income	$ 0.96	$ 1.38	$ 1.49	$ 0.40	$ 0.70	$ 1.27	$ 1.26	$ 0.16	$ 4.23	$ 3.39	$ 1.75