Mortgage Loans by Property Type and Geographic Region (Detail) - USD ($) $ in Millions		Sep. 30, 2025	Dec. 31, 2024
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	[1],[2]	$ 2,129.8	$ 2,224.5
Mortgage Loans, Percent of Total	[2]	100.00%	100.00%
New England
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 50.6	$ 52.6
Mortgage Loans, Percent of Total		2.40%	2.40%
Mid-Atlantic
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 161.7	$ 167.2
Mortgage Loans, Percent of Total		7.60%	7.50%
East North Central
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 275.7	$ 297.2
Mortgage Loans, Percent of Total		12.90%	13.40%
West North Central
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 145.6	$ 151.1
Mortgage Loans, Percent of Total		6.80%	6.80%
South Atlantic
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 508.1	$ 532.5
Mortgage Loans, Percent of Total		23.90%	23.90%
East South Central
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 86.5	$ 95.1
Mortgage Loans, Percent of Total		4.10%	4.30%
West South Central
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 184.8	$ 193.6
Mortgage Loans, Percent of Total		8.70%	8.70%
Mountain
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 271.5	$ 278.7
Mortgage Loans, Percent of Total		12.70%	12.50%
Pacific
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 445.3	$ 456.5
Mortgage Loans, Percent of Total		20.90%	20.50%
Apartment
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 657.1	$ 658.2
Mortgage Loans, Percent of Total		30.90%	29.60%
Industrial
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 662.0	$ 690.4
Mortgage Loans, Percent of Total		31.10%	31.00%
Office
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 319.9	$ 338.4
Mortgage Loans, Percent of Total		15.00%	15.20%
Retail
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 462.9	$ 496.2
Mortgage Loans, Percent of Total		21.70%	22.30%
Other Property
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 27.9	$ 41.3
Mortgage Loans, Percent of Total		1.30%	1.90%

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

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