Debt ( Details Textuals) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Fees to maintain credit lines	$ 6.0	$ 2.2
Ratio of combined earnings and fixed earnings to fixed charges required to maintain availability of credit line	1.25
Line of credit facility financial covenants combined earnings and fixed charges to fixed charges ratio actual	1.5
Average Commercial Paper Outstanding	$ 1,076.0	491.0
Total Interest Paid on short and long term debt	500.0	300.0	$ 300.0
Long Term Debt [Member] | ParentCompanyMember
Debt Instrument [Line Items]
Total bank lines of credit of the company	3,500.0	3,000.0
Unutilized total credit lines	$ 3,500.0	$ 3,000.0