Schedule IV Reinsurance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Reinsurance Premiums for Insurance Companies, by Product Segment
Direct Premiums, Life Insurance in Force	$ 1,162,098.7	$ 1,079,042.5	$ 1,057,312.2
Ceded Premiums, Life Insurance in Force	24,373.3	21,210.7	35,773.9
Assumed Premiums, Life Insurance in Force	1,009.8	921.6	931.9
Premiums, Net, Life Insurance in Force	$ 1,138,735.2	$ 1,058,753.4	$ 1,022,470.2
Life Insurance in Force Premiums, Percentage Assumed to Net	0.10%	0.10%	0.10%
Gross Amount	$ 10,732.1	$ 10,286.8	$ 9,893.6
Reinsurance Ceded	304.5	321.2	355.8
Assumed Premiums Earned	69.8	80.4	78.7
Net Amount	$ 10,497.4	$ 10,046.0	$ 9,616.5
Percentage of Amount Assumed to Net	0.70%	0.80%	0.80%
Life Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross Amount	$ 3,011.1	$ 2,799.0	$ 2,704.3
Reinsurance Ceded	159.0	157.5	155.1
Assumed Premiums Earned	5.1	6.0	6.5
Net Amount	$ 2,857.2	$ 2,647.5	$ 2,555.7
Percentage of Amount Assumed to Net	0.20%	0.20%	0.30%
Accident, Health, and Other Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross Amount	$ 7,721.0	$ 7,487.8	$ 7,189.3
Reinsurance Ceded	145.5	163.7	200.7
Assumed Premiums Earned	64.7	74.4	72.2
Net Amount	$ 7,640.2	$ 7,398.5	$ 7,060.8
Percentage of Amount Assumed to Net	0.80%	1.00%	1.00%