Acquisition Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Business Combinations [Abstract]
After-tax acquisition costs	$ 53.9	$ 3.0	$ 62.3	$ 3.0
After-tax acquisition costs (per share)	$ 0.24	$ 0.01	$ 0.28	$ 0.01
Operating Revenues	$ 1,629.2	$ 1,879.5	$ 4,180.1	$ 5,208.2
Net Income	$ 159.1	$ 143.2	$ 488.7	$ 499.5
Earnings per share (Basic)	$ 0.50	$ 0.46	$ 1.55	$ 1.54
Earnings per share (Diluted)	$ 0.50	$ 0.45	$ 1.54	$ 1.53