Long-Term Debt - Long-Term Debt (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Total debt	$ 5,119.5	$ 2,625.8
Less: Current maturities of long-term debt	(20.1)
Long-term debt	5,099.4	2,625.8
0.650% Senior Notes, Due 2023
Debt Instrument [Line Items]
Total debt	696.9
4.25% Senior Notes, Due 2024
Debt Instrument [Line Items]
Total debt	398.1	397.6
7% Debentures, Due 2025
Debt Instrument [Line Items]
Total debt	124.5	124.5
3.450% Senior Notes, Due 2027
Debt Instrument [Line Items]
Total debt	297.9	297.6
3.500% Senior Notes, Due 2027
Debt Instrument [Line Items]
Total debt	496.2	495.8
2.500% Senior Notes, Due 2030
Debt Instrument [Line Items]
Total debt	490.9	490.1
2.400% Senior Notes, Due 2031
Debt Instrument [Line Items]
Total debt	891.7
6.25% Senior Notes, Due 2037
Debt Instrument [Line Items]
Total debt	228.3	228.2
4.250% Senior Notes, Due 2047
Debt Instrument [Line Items]
Total debt	592.0	591.9
3.200% Senior Notes, Due 2051
Debt Instrument [Line Items]
Total debt	882.9
Trade Receivable Facility
Debt Instrument [Line Items]
Total debt	20.0
Other Notes
Debt Instrument [Line Items]
Total debt	$ 0.1	$ 0.1

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