Long-Term Debt - Long-Term Debt (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Total debt	$ 5,102.4	$ 5,100.9
Less: Current maturities	(0.1)	(0.1)
Long-term debt	5,102.3	5,100.8
0.650% Senior Notes, Due 2023
Debt Instrument [Line Items]
Total debt	697.8	697.4
4.25% Senior Notes, Due 2024
Debt Instrument [Line Items]
Total debt	398.4	398.3
7% Debentures, Due 2025
Debt Instrument [Line Items]
Total debt	124.6	124.6
3.450% Senior Notes, Due 2027
Debt Instrument [Line Items]
Total debt	298.0	297.9
3.500% Senior Notes, Due 2027
Debt Instrument [Line Items]
Total debt	496.5	496.4
2.500% Senior Notes, Due 2030
Debt Instrument [Line Items]
Total debt	491.4	491.1
2.400% Senior Notes, Due 2031
Debt Instrument [Line Items]
Total debt	892.1	891.8
6.25% Senior Notes, Due 2037
Debt Instrument [Line Items]
Total debt	228.3	228.3
4.250% Senior Notes, Due 2047
Debt Instrument [Line Items]
Total debt	592.1	592.1
3.200% Senior Notes, Due 2051
Debt Instrument [Line Items]
Total debt	883.1	882.9
Other Notes
Debt Instrument [Line Items]
Total debt	$ 0.1	$ 0.1

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