Capital Stock (Summary of Cash Dividend Activity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2015	Jun. 30, 2014
Capital [Abstract]
Declaration date	Apr. 28, 2015	Jan. 27, 2015	Apr. 29, 2014	Jan. 28, 2014
Record date	Jun. 10, 2015	Mar. 10, 2015	Jun. 10, 2014	Mar. 10, 2014
Payment date	Jun. 25, 2015	Mar. 25, 2015	Jun. 25, 2014	Mar. 25, 2014
Cash dividends per share	$ 0.6250	$ 0.6250	$ 0.4375	$ 0.4375
Total payment	$ 163.9	$ 166.6	$ 120.5	$ 123.4	$ 330.5	$ 243.9