Schedule IV Reinsurance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reinsurance Premiums for Insurance Companies, by Product Segment
Direct Premiums, Life Insurance in Force	$ 1,057,312.2	$ 1,007,562.2	$ 979,755.7
Ceded Premiums, Life Insurance in Force	35,773.9	37,794.6	41,550.9
Assumed Premiums, Life Insurance in Force	931.9	920.3	896.4
Premiums, Net, Life Insurance in Force	$ 1,022,470.2	$ 970,687.9	$ 939,101.2
Life Insurance in Force Premiums, Percentage Assumed to Net	0.10%	0.10%	0.10%
Gross Amount	$ 9,900.5	$ 9,742.8	$ 9,621.9
Reinsurance Ceded	355.8	352.4	337.9
Assumed Premiums Earned	78.7	90.6	94.1
Net Amount	$ 9,623.4	$ 9,481.0	$ 9,378.1
Percentage of Amount Assumed to Net	0.80%	1.00%	1.00%
Life Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross Amount	$ 2,711.2	$ 2,550.7	$ 2,536.8
Reinsurance Ceded	155.1	150.2	141.9
Assumed Premiums Earned	6.5	7.6	8.0
Net Amount	$ 2,562.6	$ 2,408.1	$ 2,402.9
Percentage of Amount Assumed to Net	0.30%	0.30%	0.30%
Accident, Health, and Other Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross Amount	$ 7,189.3	$ 7,192.1	$ 7,085.1
Reinsurance Ceded	200.7	202.2	196.0
Assumed Premiums Earned	72.2	83.0	86.1
Net Amount	$ 7,060.8	$ 7,072.9	$ 6,975.2
Percentage of Amount Assumed to Net	1.00%	1.20%	1.20%