Capital Stock (Cash Dividend Activity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Dividends, Cash [Abstract]
Declaration Date	Nov. 01, 2016	Jul. 26, 2016	Apr. 26, 2016	Feb. 18, 2016	Oct. 27, 2015	Jul. 28, 2015	Apr. 28, 2015	Jan. 27, 2015
Record Date	Dec. 05, 2016	Sep. 09, 2016	Jun. 10, 2016	Mar. 10, 2016	Dec. 04, 2015	Sep. 10, 2015	Jun. 10, 2015	Mar. 10, 2015
Payment Date	Dec. 21, 2016	Sep. 26, 2016	Jun. 24, 2016	Mar. 25, 2016	Dec. 21, 2015	Sep. 25, 2015	Jun. 25, 2015	Mar. 25, 2015
Cash Dividend per Share	$ 0.6500	$ 0.6500	$ 0.6500	$ 0.6500	$ 0.6250	$ 0.6250	$ 0.6250	$ 0.6250
Total	$ 171.3	$ 171.1	$ 170.9	$ 170.7	$ 163.1	$ 163.0	$ 163.9	$ 166.6	$ 684.0	$ 656.6	$ 480.7