Debt (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Credit Facilities [Abstract]
Available and unused credit lines	$ 3,749.5	$ 3,681.0
Short-Term Borrowings [Abstract]
Short-term debt	11.3	11.8
Long-Term Debt [Abstract]
Long-term debt, carrying amount	4,900.0	4,900.0
Unamortized premium (discount), net	5.3	6.2
Unamortized debt issuance costs	(17.4)	(20.3)
Unamortized deferred gain from settlement of interest rate swaps	52.6	66.4
Fair value adjustment attributed to outstanding interest rate swaps	(83.3)	(39.4)
Long-term debt, total	4,857.2	4,912.9
Long-term debt, current portion	(499.4)	0.0
Long-Term Debt	4,357.8	4,912.9
Interest Rate Swaps on 2024 Notes [Member]
Long-Term Debt [Abstract]
Interest rate swaps, liability, at fair value	39.4
Interest rate swaps, notional amount	750.0
Interest Rate Swaps on 2026 Notes [Member]
Long-Term Debt [Abstract]
Interest rate swaps, liability, at fair value	43.9
Interest rate swaps, notional amount	500.0
Credit Facility
Credit Facilities [Abstract]
Credit Facility, maximum borrowing capacity	$ 2,500.0
Credit Facility, expiration date	Jul. 31, 2021
Available and unused credit lines	$ 2,500.0	2,500.0
Credit Facility, covenant terms	The Credit Facility contains financial covenants that require us to maintain a Leverage Ratio of consolidated indebtedness to consolidated EBITDA of no more than 3 times for the most recently ended 12-month period (EBITDA is defined as earnings before interest, taxes, depreciation and amortization) and an Interest Coverage Ratio of consolidated EBITDA to interest expense of at least 5 times for the most recently ended 12-month period.
Credit Facility, covenant compliance	At September 30, 2018 we were in compliance with these covenants as our Leverage Ratio was 2.0 times and our Interest Coverage Ratio was 10.2 times.
Commercial Paper [Member]
Credit Facilities [Abstract]
Credit Facility, maximum borrowing capacity	$ 2,000.0
Uncommitted credit lines
Credit Facilities [Abstract]
Available and unused credit lines	1,249.5	1,181.0
6.25% Senior Notes due 2019
Long-Term Debt [Abstract]
Long-term debt, carrying amount	$ 500.0	500.0
Long-term debt, interest rate	6.25%
Long-term debt, maturity date	Jul. 15, 2019
4.45% Senior Notes due 2020
Long-Term Debt [Abstract]
Long-term debt, carrying amount	$ 1,000.0	1,000.0
Long-term debt, interest rate	4.45%
Long-term debt, maturity date	Aug. 15, 2020
3.625% Senior Notes due 2022
Long-Term Debt [Abstract]
Long-term debt, carrying amount	$ 1,250.0	1,250.0
Long-term debt, interest rate	3.625%
Long-term debt, maturity date	May 01, 2022
3.65% Senior Notes due 2024
Long-Term Debt [Abstract]
Long-term debt, carrying amount	$ 750.0	750.0
Long-term debt, interest rate	3.65%
Long-term debt, maturity date	Nov. 01, 2024
3.60% Senior Notes due 2026
Long-Term Debt [Abstract]
Long-term debt, carrying amount	$ 1,400.0	$ 1,400.0
Long-term debt, interest rate	3.60%
Long-term debt, maturity date	Apr. 15, 2026

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

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