Investment Gains and Losses Reported in Consolidated Statements of Income (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022		Sep. 30, 2021
Fixed Maturity Securities
Gross Gains on Sales	$ 0.0	$ 1.3	$ 0.8	[1]	$ 74.9
Gross Losses on Sales	(13.4)	(5.4)	(26.4)		(9.0)
Credit Losses	(0.5)	0.0	(4.6)		(9.3)
Mortgage Loans and Other Invested Assets
Gross Gains on Sales	0.0	1.5	1.4		5.0
Credit Losses	0.4	0.0	0.3		(1.6)
All other investment gains and losses
Embedded Derivative in Modified Coinsurance Arrangement	14.9	2.6	10.7		21.2
All Other Derivatives	(0.9)	0.7	4.6		2.3
Foreign Currency Transactions	(4.1)	(0.8)	(8.5)		(1.3)
Net Investment Gain (Loss)	$ (4.4)	$ (0.1)	$ (22.3)		85.4
Closed Block Individual Disability Reinsurance Transaction | Phase 2
All other investment gains and losses
Net Investment Gain (Loss)					$ 67.6

[1] 1Gross gains on sales of fixed maturity securities for the nine months ended September 30, 2021 includes gains of $67.6 million as a result of the second phase of the reinsurance transaction that we completed during the first quarter of 2021. See Note 12 for further discussion.