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Credit and Other Debt Agreements - Note Purchase Agreements - Additional Information (Detail) - USD ($) $ in Millions |  |  |  | 12 Months Ended |
--- | --- | --- | --- | --- | ---
May 05, 2021 | Feb. 10, 2021 | Jan. 30, 2020 | Dec. 31, 2021 | Dec. 31, 2020
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 |
Fixed Rate of 5.18%, Balloon Due February 10, 2021 [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Debt instrument, interest rate |  |  |  |  | 5.18%
Note Purchase Agreements [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Realized a cash gain (loss) on hedging transaction | $ (17.2) | $ (22.9) | $ (8.9) |  |
Derivative instrument, term | 10 years | 10 years | 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] | Fixed Rate of 5.18%, Balloon Due February 10, 2021 [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Repayments of debt |  | $ 75.0 |  |  |
Note Purchase Agreements [Member] | Private Placement [Member] | Unsecured Notes [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Notes issued and sold | $ 75.0 | $ 100.0 | $ 575.0 |  |
Weighted average maturity of notes | 15 years | 15 years | 11 years 8 months 12 days |  |
Weighted average interest rate of notes | 3.98% | 3.97% | 4.23% |  |
Debt instrument, interest rate | 2.46% | 2.44% |  |  |
Debt instrument, due date | 2036 | 2036 |  |  |

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- Definition Amount Payable to Redeem the Notes, Percent of the Principal Amount + References No definition available. + Details
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- Definition Discount Rate used to Compute the Remaining Scheduled Payments of Principal and Interest + References No definition available. + Details
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1B -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition 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. + References No definition available. + Details
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