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Credit and Other Debt Agreements - Senior Notes - Additional Information (Detail) - USD ($) $ in Millions |  |  | 12 Months Ended
--- | --- | --- | ---
Nov. 09, 2021 | May 20, 2021 | Dec. 31, 2021
Debt Instrument [Line Items] |  |  |
Loss on extinguishment of debt |  |  | $ 16.2
Fixed Rate of 3.50%, Balloon Due May 20, 2051 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Periodic payment of interest |  |  | 3.50%
Fixed Rate of 2.40%, Balloon Due November 9, 2031 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Periodic payment of interest |  |  | 2.40%
Fixed Rate of 3.05%, Balloon Due March 9, 2052 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Periodic payment of interest |  |  | 3.05%
Unsecured Senior Notes [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Notes issued and sold | $ 750.0 | $ 1,500.0 |
Weighted average interest rate | 2.80% | 3.31% |
Realized a cash gain (loss) on hedging transaction |  | $ (57.8) |
Derivative instrument, term |  | 10 years |
Unsecured Senior Notes [Member] | Fixed Rate of 2.50%, Balloon Due May 20, 2031 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Notes issued and sold |  | $ 650.0 |
Periodic payment of interest |  | 2.50% |
Periodic payments of interest and principal, expiry year |  | 2031 |
Amount payable to redeem the notes, percent of the principal amount following transaction termination event |  | 101.00% |
Number of days to occur reinsurance transaction termination event for note redemption |  | 30 days |
Notes redemption date |  | Aug. 13, 2021 |
Loss on extinguishment of debt |  | $ 16.2 |
Redemption premium |  | 6.5 |
Unamortized discount amount debt issuance and write-off debt acquisition costs |  | 9.7 |
Unsecured Senior Notes [Member] | Fixed Rate of 3.50%, Balloon Due May 20, 2051 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Notes issued and sold |  | $ 850.0 |
Periodic payment of interest |  | 3.50% |
Periodic payments of interest and principal, expiry year |  | 2051 |
Unsecured Senior Notes [Member] | Fixed Rate of 2.40%, Balloon Due November 9, 2031 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Notes issued and sold | $ 400.0 |  |
Periodic payment of interest | 2.40% |  |
Periodic payments of interest and principal, expiry year | 2031 |  |
Unsecured Senior Notes [Member] | Fixed Rate of 3.05%, Balloon Due March 9, 2052 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Notes issued and sold | $ 350.0 |  |
Periodic payment of interest | 3.05% |  |
Periodic payments of interest and principal, expiry year | 2052 |  |

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