Long-Term Debt - Schedule of Principal Amount, Effective Interest Rate and Maturity Date for Corporation's Senior Notes (Detail) - USD ($)	12 Months Ended
Dec. 31, 2020	Mar. 05, 2020
4.25% Senior Notes, Due 2024
Debt Instrument [Line Items]
Principal Amount	$ 400,000,000.0
Effective Interest Rate	4.25%
Maturity Date	Jul. 02, 2024
7% Debentures, Due 2025
Debt Instrument [Line Items]
Principal Amount	$ 125,000,000.0
Effective Interest Rate	7.12%
Maturity Date	Dec. 01, 2025
3.450% Senior Notes, Due 2027
Debt Instrument [Line Items]
Principal Amount	$ 300,000,000.0
Effective Interest Rate	3.47%
Maturity Date	Jun. 01, 2027
3.500% Senior Notes, Due 2027
Debt Instrument [Line Items]
Principal Amount	$ 500,000,000.0
Effective Interest Rate	3.53%
Maturity Date	Dec. 15, 2027
2.500% Senior Notes, Due 2030
Debt Instrument [Line Items]
Principal Amount	$ 500,000,000.0	$ 500,000,000
Effective Interest Rate	2.71%
Maturity Date	Mar. 15, 2030
6.25% Senior Notes, Due 2037
Debt Instrument [Line Items]
Principal Amount	$ 230,000,000.0
Effective Interest Rate	6.45%
Maturity Date	May 01, 2037
4.250% Senior Notes, Due 2047
Debt Instrument [Line Items]
Principal Amount	$ 600,000,000.0
Effective Interest Rate	4.27%
Maturity Date	Dec. 15, 2047

Face (par) amount of debt instrument at time of issuance.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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