Debt Financing - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Line Items]
Weighted-average interst rate on short-term borrowings	2.60%	2.50%
Debt, face amount	$ 3,794.5	$ 4,727.5	$ 3,779.5
Additional paid-in capital	7,376.0	7,072.4
Revolving Credit Facility Expiring In Twenty Nineteen | Unused lines of Credit [Member]
Debt Disclosure [Line Items]
Unused Line of credit	$ 3,500.0
Unused Line of credit agreement, fees	0.08%
Line of Credit Facility, Commitment Fee Description	Fees and interest rates on this line are primarily based on the Company’s long-term credit rating assigned by Moody’s and Standard & Poor’s
Outside the U.S.
Debt Disclosure [Line Items]
Foreign currency bank line borrowings	$ 253.5	$ 268.0
Outside the U.S. | Unused lines of Credit [Member]
Debt Disclosure [Line Items]
Line of Credit Facility, Currency	denominated in various currencies
Line of Credit Facility, Interest Rate Description	local market rates of interest
U.S.
Debt Disclosure [Line Items]
Commercial Paper	$ 99.9