Schedule IV Reinsurance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Reinsurance Premiums for Insurance Companies, by Product Segment
Direct Premiums, Life Insurance in Force	$ 1,296,061.4	$ 1,162,098.7	$ 1,079,042.5
Ceded Premiums, Life Insurance in Force	28,606.8	24,373.3	21,210.7
Assumed Premiums, Life Insurance in Force	992.3	1,009.8	921.6
Premiums, Net, Life Insurance in Force	$ 1,268,446.9	$ 1,138,735.2	$ 1,058,753.4
Life Insurance in Force Premiums, Percentage Assumed to Net	0.10%	0.10%	0.10%
Gross Amount	$ 11,064.0	$ 10,732.1	$ 10,286.8
Reinsurance Ceded	287.5	304.5	321.2
Assumed Premiums Earned	54.5	69.8	80.4
Net Amount	$ 10,831.0	$ 10,497.4	$ 10,046.0
Percentage of Amount Assumed to Net	0.50%	0.70%	0.80%
Life Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross Amount	$ 3,216.8	$ 3,011.1	$ 2,799.0
Reinsurance Ceded	147.5	159.0	157.5
Assumed Premiums Earned	5.3	5.1	6.0
Net Amount	$ 3,074.6	$ 2,857.2	$ 2,647.5
Percentage of Amount Assumed to Net	0.20%	0.20%	0.20%
Accident, Health, and Other Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross Amount	$ 7,847.2	$ 7,721.0	$ 7,487.8
Reinsurance Ceded	140.0	145.5	163.7
Assumed Premiums Earned	49.2	64.7	74.4
Net Amount	$ 7,756.4	$ 7,640.2	$ 7,398.5
Percentage of Amount Assumed to Net	0.60%	0.80%	1.00%