Debt ( Details Textuals) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Fees to maintain credit lines	$ 2.2	$ 25.8
Line of credit facility financial covenants combined earnings and fixed charges to fixed charges ratio required	1.25
Line of credit facility financial covenants combined earnings and fixed charges to fixed charges ratio actual	1.62
Average Commercial Paper Outstanding	$ 491.0	943.0
Short Term Debt [Member]
Debt Instrument [Line Items]
Total Interest Paid	11.0	3.5	$ 0.3
Total bank lines of credit of the company	3,000.0	3,000.0
Unutilized total credit lines	3,000.0	3,000.0
Long-term Debt [Member]
Debt Instrument [Line Items]
Total Interest Paid	$ 300.0	$ 300.0	$ 500.0