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Credit and Other Debt Agreements - Credit Agreement - Additional Information (Detail) $ in Millions, $ in Millions |  | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Jun. 22, 2023 USD ($) | Dec. 31, 2024 AUD ($) | Dec. 31, 2024 NZD ($) | Dec. 31, 2024 USD ($) | Dec. 31, 2024 AUD ($) | Dec. 31, 2024 NZD ($) | Dec. 31, 2023 USD ($) | Nov. 07, 2023 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Total liabilities |  |  |  | $ 44,075,600,000 |  |  | $ 40,800,500,000 |
Long-term debt |  |  |  | 23,000,000.0 |  |  |  |
Revolving Credit Facility [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Credit facility, term | 5 years |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity | $ 1,200,000,000 |  |  |  |  |  |  | $ 1,700,000,000
Line of credit facility, amount outstanding |  |  |  | 225,200,000 |  |  |  |
Interest rate for facility |  | The interest rates on Facility B are Interbank rates, which vary by tranche, duration and currency, plus a margin of 1.400% and 1.850% for the AU$ and NZ$ tranches, respectively. The interest rates on Facilities C and D are 30 day Interbank rates, plus a margin of 0.830% and 0.990% for the AU$ and NZ$ tranches, respectively. The annual fee for Facility B is 0.56% and 0.8325% for the undrawn commitments for the AU$ and NZ$ tranches, respectively. The annual fee for Facility C is 0.77% and for Facility D is 0.90% of the total commitments of the facilities | The interest rates on Facility B are Interbank rates, which vary by tranche, duration and currency, plus a margin of 1.400% and 1.850% for the AU$ and NZ$ tranches, respectively. The interest rates on Facilities C and D are 30 day Interbank rates, plus a margin of 0.830% and 0.990% for the AU$ and NZ$ tranches, respectively. The annual fee for Facility B is 0.56% and 0.8325% for the undrawn commitments for the AU$ and NZ$ tranches, respectively. The annual fee for Facility C is 0.77% and for Facility D is 0.90% of the total commitments of the facilities |  |  |  |  |
Debt instrument fair value amount |  |  |  | 225,200,000 |  |  |  |
Letter of Credit Sub-facility [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity | $ 75,000,000 |  |  |  |  |  |  |
Credit Facility Two [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Line of credit facility, amount outstanding |  |  |  |  | $ 350.0 | $ 0.0 |  |
Line of credit facility, remaining borrowing capacity |  |  |  |  | 60.0 | 25.0 |  |
Net borrowings on premium financing debt facility |  | $ 410.0 | $ 25.0 |  |  |  |  |
Credit Facility Three [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Line of credit facility, amount outstanding |  |  |  |  | 0.0 |  |  |
Line of credit facility, remaining borrowing capacity |  |  |  |  | $ 60.0 |  |  |
Net borrowings on premium financing debt facility |  | $ 390.0 | $ 10.0 |  |  |  |  |
Annual fee percentage |  | 0.77% | 0.77% |  |  |  |  |
Credit Facility Four [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Line of credit facility, amount outstanding |  |  |  |  |  | 12.5 |  |
Line of credit facility, remaining borrowing capacity |  |  |  |  |  | $ 2.5 |  |
Net borrowings on premium financing debt facility |  | $ 60.0 | $ 15.0 |  |  |  |  |
Annual fee percentage |  | 0.90% | 0.90% |  |  |  |  |
AUD Denominated Tranche [Member] | Revolving Credit Facility [Member] | Facility B [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Additional margin percentage on interest rate |  | 1.40% | 1.40% |  |  |  |  |
Annual fee percentage |  | 0.56% | 0.56% |  |  |  |  |
AUD Denominated Tranche [Member] | Revolving Credit Facility [Member] | Facility C and D [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Additional margin percentage on interest rate |  | 0.83% | 0.83% |  |  |  |  |
NZD Denominated Tranche [Member] | Revolving Credit Facility [Member] | Facility B [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Additional margin percentage on interest rate |  | 1.85% | 1.85% |  |  |  |  |
Annual fee percentage |  | 0.8325% | 0.8325% |  |  |  |  |
NZD Denominated Tranche [Member] | Revolving Credit Facility [Member] | Facility C and D [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Additional margin percentage on interest rate |  | 0.99% | 0.99% |  |  |  |  |
Note Purchase Agreements [Member] | Level 3 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Line of credit facility, fair value of amount outstanding |  |  |  | 12,072,700,000 |  |  |  |
Long-term debt |  |  |  | 13,073,000,000 |  |  |  |
Unsecured Multicurrency Credit Agreement [Member] | Standby Letters of Credit [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  |  |  | 1,689,100,000 |  |  |  |
Line of credit facility, amount outstanding |  |  |  | 10,900,000 |  |  |  |
Total liabilities |  |  |  | 12,000,000 |  |  |  |
Line of credit facility, fair value of amount outstanding |  |  |  | $ 0 |  |  |  |
Unsecured Multicurrency Credit Agreement [Member] | Minimum [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Interest rates on base rate loans |  | 0.00% | 0.00% |  |  |  |  |
Fixed rate over SOFR rate, eurocurrency rate or RFR rate |  | 0.775% | 0.775% |  |  |  |  |
Annual facility fee of revolving credit facility |  | 0.10% | 0.10% |  |  |  |  |
Unsecured Multicurrency Credit Agreement [Member] | Maximum [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Interest rates on base rate loans |  | 0.375% | 0.375% |  |  |  |  |
Fixed rate over SOFR rate, eurocurrency rate or RFR rate |  | 1.375% | 1.375% |  |  |  |  |
Annual facility fee of revolving credit facility |  | 0.25% | 0.25% |  |  |  |  |

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