Investment Gains and Losses Reported in Consolidated Statements of Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Realized Investment Gains and Losses Reported in Consolidated Statements of Income [Abstract]
Embedded Derivative in Modified Coinsurance Arrangement	$ (3.4)	$ 16.9
All Other Derivatives	1.8	1.7
Foreign Currency Transactions	(1.5)	(0.1)
Net Investment Gain (Loss)	(13.8)	84.6
Mortgage Loans and Other Invested Assets
Gross Gains on Sales	1.4	2.5
Gross Losses on Sales	0.0	0.0
Credit Losses	0.5	1.7
Fixed Maturity Securities
Gross Gains on Sales	0.3	71.3	[1]
Gross Losses on Sales	8.8	1.1
Credit Losses	$ (4.1)	$ (8.3)

[1] Gross gains on sales of fixed maturity securities for the three months ended March 31, 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.