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Credit and Other Debt Agreements - Note Purchase Agreements - Additional Information (Detail) - USD ($) $ in Millions					12 Months Ended
	Jan. 30, 2020	Dec. 02, 2019	Jun. 12, 2019	Feb. 13, 2019	Dec. 31, 2020	Dec. 31, 2019
Fixed Rate of 4.72%, Balloon due February 13, 2024 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 100.0
Debt instrument, interest rate					4.72%	4.72%
Debt instrument, due date					2024
Fixed Rate of 4.85%, Balloon due February 13, 2026 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 140.0
Debt instrument, interest rate					4.85%	4.85%
Debt instrument, due date					2026
Fixed Rate of 5.04%, Balloon due February 13, 2029 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 100.0
Debt instrument, interest rate					5.04%	5.04%
Debt instrument, due date					2029
Fixed Rate of 5.14%, Balloon due March 13, 2031 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 180.0
Debt instrument, interest rate					5.14%	5.14%
Debt instrument, due date					2031
Fixed Rate of 5.29%, balloon due March 13, 2034 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 40.0
Debt instrument, interest rate					5.29%	5.29%
Debt instrument, due date					2034
Fixed Rate of 5.45%, balloon due March 13, 2039 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 40.0
Debt instrument, interest rate					5.45%	5.45%
Debt instrument, due date					2039
Fixed Rate of 3.75% Senior Notes Due in 2027 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 30.0
Debt instrument, interest rate					3.75%
Debt instrument, due date					2027
Fixed Rate of 3.99% Senior Notes Due in 2030 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 341.0
Debt instrument, interest rate					3.99%
Debt instrument, due date					2030
Fixed Rate of 4.09% Senior Notes Due in 2032 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 69.0
Debt instrument, interest rate					4.09%
Debt instrument, due date					2032
Fixed Rate of 4.24% Senior Notes Due in 2035 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 79.0
Debt instrument, interest rate					4.24%
Debt instrument, due date					2035
Fixed Rate of 4.49% Senior Notes Due in 2040 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 56.0
Debt instrument, interest rate					4.49%
Debt instrument, due date					2040
Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Realized a cash gain on hedging transaction	$ 8.9		$ 5.2	$ 1.2
Derivative instrument, term	10 years
Amount payable to redeem the notes, percent of the principal amount					100.00%
Discount rate used to compute the remaining scheduled payments of principal and interest					U.S. Treasury yield plus 0.5
Note Purchase Agreements [Member] | Senior Unsecured Notes [Member] | Private Placement [Member]
Debt Instrument [Line Items]
Notes issued and sold				600.0
Note Purchase Agreements [Member] | Fixed Rate Senior Unsecured Notes [Member] | Private Placement [Member] | Tranche One [Member]
Debt Instrument [Line Items]
Notes issued and sold				340.0
Note Purchase Agreements [Member] | Fixed Rate Senior Unsecured Notes [Member] | Private Placement [Member] | Tranche Two [Member]
Debt Instrument [Line Items]
Notes issued and sold				$ 260.0
Note Purchase Agreements [Member] | Unsecured Notes [Member]
Debt Instrument [Line Items]
Weighted average interest rate of notes				5.04%
Note Purchase Agreements [Member] | Unsecured Notes [Member] | Private Placement [Member]
Debt Instrument [Line Items]
Notes issued and sold	$ 575.0	$ 50.0	$ 175.0
Weighted average maturity of notes	11 years 8 months 12 days
Weighted average interest rate of notes	4.23%	3.48%
Debt instrument, interest rate			4.48%
Debt instrument, due date		2029	2034
Note Purchase Agreements [Member] | Unsecured Notes [Member] | Private Placement [Member] | Weighted Average [Member]
Debt Instrument [Line Items]
Weighted average maturity of notes				10 years 1 month 6 days
Note Purchase Agreements [Member] | Series K Notes [Member]
Debt Instrument [Line Items]
Notes issued and sold			$ 50.0
Weighted average interest rate of notes			4.68%
Note Purchase Agreements [Member] | Series C Notes [Member]
Debt Instrument [Line Items]
Notes issued and sold		$ 50.0

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- Definition

Amount Payable to Redeem the Notes, Percent of the Principal Amount

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Debt Instrument Maturity Year

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Contractual interest rate for funds borrowed, under the debt agreement.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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