Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Apr. 06, 2016	Oct. 31, 2015
Credit Facilities [Abstract]
Available and unused credit lines	$ 3,681.0	$ 3,632.0
Short-Term Borrowings [Abstract]
Short-term debt	$ 11.8	$ 28.7
Short-term borrowings, weighted average interest rate	2.60%	9.80%
Long-Term Debt [Abstract]
Long-term debt, carrying amount	$ 4,900.0	$ 4,900.1
Unamortized premium (discount), net	6.2	7.6
Unamortized debt issuance costs	(20.3)	(24.2)
Unamortized deferred gain from settlement of interest rate swaps	66.4	84.7
Fair value adjustment attributed to outstanding interest rate swaps	(39.4)	(47.6)
Long-term debt, total	4,912.9	4,920.6
Long-term debt, current portion	0.0	(0.1)
Long-Term Debt	4,912.9	4,920.5
Components of Interest Expense [Abstract]
Interest expense, Long-term debt	201.6	205.5	$ 210.2
Interest expense, Interest rate swaps	(7.2)	(13.1)	(44.1)
Interest expense, Amortization of deferred gain on interest rate swaps	(12.9)	(15.4)	(9.2)
Interest expense, Commercial paper	12.5	6.8	4.8
Interest expense, Fees	5.6	5.6	5.7
Interest expense, Other	24.9	20.3	13.7
Interest expense, total	224.5	209.7	$ 181.1
Contractual Maturities of Long-Term Debt [Abstract]
Contractual maturities of long-term debt, 2018	0.0
Contractual maturities of long-term debt, 2019	500.0
Contractual maturities of long-term debt, 2020	1,000.0
Contractual maturities of long-term debt, 2021	0.0
Contractual maturities of long-term debt, 2022	1,250.0
Contractual maturities of long-term debt, Thereafter	2,150.0
Contractual maturities of long-term debt	4,900.0
Interest Rate Swaps on 2024 Notes [Member]
Long-Term Debt [Abstract]
Interest rate swaps, notional amount					$ 750.0
Interest rate swaps, fixed interest rate					3.65%
Interest rate swaps, liability, at fair value	14.7	17.1
Interest Rate Swaps on 2024 Notes [Member] | LIBOR [Member]
Long-Term Debt [Abstract]
Interest rate swaps, variable interest rate spread					1.72%
Interest Rate Swaps on 2026 Notes [Member]
Long-Term Debt [Abstract]
Interest rate swaps, notional amount				$ 500.0
Interest rate swaps, fixed interest rate				3.60%
Interest rate swaps, liability, at fair value	24.7	30.5
Interest Rate Swaps on 2026 Notes [Member] | LIBOR [Member]
Long-Term Debt [Abstract]
Interest rate swaps, variable interest rate spread				1.982%
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 December 31, 2017 we were in compliance with these covenants as our Leverage Ratio was 2.1 times and our Interest Coverage Ratio was 10.4 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	1,181.0	1,132.0
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
Other debt
Long-Term Debt [Abstract]
Long-term debt, carrying amount	$ 0.0	$ 0.1