Debt (Details) € in Millions, $ in Millions	3 Months Ended
Mar. 31, 2019 EUR (€)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Credit Facilities [Abstract]
Available and unused credit lines		$ 3,979.3	$ 3,731.6
Short-Term Borrowings [Abstract]
Short-term debt	€ 520	595.4	8.1
Long-Term Debt [Abstract]
Long-term debt, carrying amount		4,900.0	4,900.0
Unamortized premium (discount), net		4.6	4.9
Unamortized debt issuance costs		(15.4)	(16.4)
Unamortized deferred gain from settlement of interest rate swaps		43.4	48.0
Fair value adjustment attributed to outstanding interest rate swaps		(30.8)	(52.8)
Long-term debt, total		4,901.8	4,883.7
Long-term debt, current portion		(499.8)	(499.6)
Long-Term Debt		4,402.0	4,384.1
Interest Rate Swaps on 2024 Notes [Member]
Long-Term Debt [Abstract]
Interest rate swaps, liability, at fair value		9.8
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		21.0
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 March 31, 2019 we were in compliance with these covenants as our Leverage Ratio was 2.3 times and our Interest Coverage Ratio was 9.8 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		1,479.3	1,231.6
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%	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%	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%	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%	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%	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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Contractual interest rate for funds borrowed, under the debt agreement.

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Identification of whether the entity has been in compliance with any credit facility debt covenants during the period.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Carrying value as of the balance sheet date of notes payable (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion.

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Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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