Schedule IV Reinsurance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reinsurance Premiums for Insurance Companies, by Product Segment
Direct Premiums, Life Insurance in Force	$ 1,007,562.2	$ 979,755.7	$ 990,371.0
Ceded Premiums, Life Insurance in Force	37,794.6	41,550.9	41,669.8
Assumed Premiums, Life Insurance in Force	920.3	896.4	1,018.4
Premiums, Net, Life Insurance in Force	$ 970,687.9	$ 939,101.2	$ 949,719.6
Life Insurance in Force Premiums, Percentage Assumed to Net	0.10%	0.10%	0.10%
Gross Amount	$ 9,742.8	$ 9,621.9	$ 9,576.3
Reinsurance Ceded	352.4	337.9	327.2
Assumed Premiums Earned	90.6	94.1	116.5
Net Amount	$ 9,481.0	$ 9,378.1	$ 9,365.6
Percentage of Amount Assumed to Net	1.00%	1.00%	1.20%
Life Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross Amount	$ 2,550.7	$ 2,536.8	$ 2,549.7
Reinsurance Ceded	150.2	141.9	137.2
Assumed Premiums Earned	7.6	8.0	8.2
Net Amount	$ 2,408.1	$ 2,402.9	$ 2,420.7
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	$ 7,192.1	$ 7,085.1	$ 7,026.6
Reinsurance Ceded	202.2	196.0	190.0
Assumed Premiums Earned	83.0	86.1	108.3
Net Amount	$ 7,072.9	$ 6,975.2	$ 6,944.9
Percentage of Amount Assumed to Net	1.20%	1.20%	1.60%