Mortgage Loans by Property Type and Geographic Region (Detail) - USD ($) $ in Millions		Sep. 30, 2026	Dec. 31, 2025
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	[1]	$ 2,053.2	$ 2,109.5
Mortgage Loans, Percent of Total	[1]	100.00%	100.00%
New England
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 51.2	$ 49.9
Mortgage Loans, Percent of Total		2.50%	2.40%
Mid-Atlantic
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 154.2	$ 159.9
Mortgage Loans, Percent of Total		7.50%	7.60%
East North Central
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 266.2	$ 275.3
Mortgage Loans, Percent of Total		13.00%	13.10%
West North Central
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 119.6	$ 135.9
Mortgage Loans, Percent of Total		5.80%	6.40%
South Atlantic
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 562.9	$ 497.2
Mortgage Loans, Percent of Total		27.40%	23.50%
East South Central
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 87.0	$ 96.7
Mortgage Loans, Percent of Total		4.20%	4.60%
West South Central
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 152.1	$ 190.5
Mortgage Loans, Percent of Total		7.40%	9.00%
Mountain
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 237.7	$ 255.3
Mortgage Loans, Percent of Total		11.60%	12.10%
Pacific
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 422.3	$ 448.8
Mortgage Loans, Percent of Total		20.60%	21.30%
Apartment
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 651.0	$ 642.5
Mortgage Loans, Percent of Total		31.70%	30.50%
Industrial
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 615.8	$ 659.0
Mortgage Loans, Percent of Total		30.00%	31.20%
Office
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 285.1	$ 313.3
Mortgage Loans, Percent of Total		13.90%	14.90%
Retail
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 474.0	$ 467.0
Mortgage Loans, Percent of Total		23.10%	22.10%
Other Property
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount		$ 27.3	$ 27.7
Mortgage Loans, Percent of Total		1.30%	1.30%

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