Short-term Debt and Lines of Credit - Short-term Borrowings (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Short-term borrowings
Commercial Paper	$ 661.5	$ 617.6
Commercial paper
Short-term borrowings
Short-term borrowings outstanding	661.5
Commercial Paper	$ 661.5
Weighted-average interest rate on commercial paper outstanding	0.32%	0.22%
Average amount of commercial paper borrowings outstanding	$ 785.6
Average Interest Rate (as a percent)	0.27%