Long-Term Debt - Long-Term Debt (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Total debt	$ 2,625.8	$ 2,773.6
Less: current maturities		(340.0)
Long-term debt	2,625.8	2,433.6
4.25% Senior Notes, Due 2024
Debt Instrument [Line Items]
Total debt	397.6	397.0
7% Debentures, Due 2025
Debt Instrument [Line Items]
Total debt	124.5	124.4
3.450% Senior Notes, Due 2027
Debt Instrument [Line Items]
Total debt	297.6	297.3
3.500% Senior Notes, Due 2027
Debt Instrument [Line Items]
Total debt	495.8	495.3
2.500% Senior Notes, Due 2030
Debt Instrument [Line Items]
Total debt	490.1
6.25% Senior Notes, Due 2037
Debt Instrument [Line Items]
Total debt	228.2	228.1
4.250% Senior Notes, Due 2047
Debt Instrument [Line Items]
Total debt	591.9	591.7
Floating Rate Senior Notes, Due 2020
Debt Instrument [Line Items]
Total debt		299.7
Trade Receivable Facility
Debt Instrument [Line Items]
Total debt		340.0
Other Notes
Debt Instrument [Line Items]
Total debt	$ 0.1	$ 0.1

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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