Mortgage Loans by Property Type and Geographic Region (Detail) - USD ($) $ in Millions		Jun. 30, 2025	Dec. 31, 2024
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	[1]	$ 2,172.5	$ 2,224.5
Mortgage Loans, Percent of Total		100.00%	100.00%
New England
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 51.3	$ 52.6
Mortgage Loans, Percent of Total		2.40%	2.40%
Mid-Atlantic
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 163.6	$ 167.2
Mortgage Loans, Percent of Total		7.50%	7.50%
East North Central
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 277.5	$ 297.2
Mortgage Loans, Percent of Total		12.80%	13.40%
West North Central
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 147.8	$ 151.1
Mortgage Loans, Percent of Total		6.80%	6.80%
South Atlantic
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 525.0	$ 532.5
Mortgage Loans, Percent of Total		24.10%	23.90%
East South Central
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 87.4	$ 95.1
Mortgage Loans, Percent of Total		4.00%	4.30%
West South Central
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 186.7	$ 193.6
Mortgage Loans, Percent of Total		8.60%	8.70%
Mountain
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 284.0	$ 278.7
Mortgage Loans, Percent of Total		13.10%	12.50%
Pacific
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 449.2	$ 456.5
Mortgage Loans, Percent of Total		20.70%	20.50%
Apartment
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 662.2	$ 658.2
Mortgage Loans, Percent of Total		30.50%	29.60%
Industrial
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 667.3	$ 690.4
Mortgage Loans, Percent of Total		30.70%	31.00%
Office
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 325.3	$ 338.4
Mortgage Loans, Percent of Total		15.00%	15.20%
Retail
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 477.2	$ 496.2
Mortgage Loans, Percent of Total		21.90%	22.30%
Other Property
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 40.5	$ 41.3
Mortgage Loans, Percent of Total		1.90%	1.90%

[1] 1Loan-to-Value Ratio utilizes the most recent internal valuation of the property