Fair Value Disclosures - Summary of the Change in Balance Sheet Carrying Value Associated with Level 3 Financial Assets Carried at Fair Value (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Changes in balance sheet carrying value associated with Level 3 financial assets carried at fair value
Balance, beginning of period	$ 12.8	$ 12.7
Total gains (losses) (realized/ unrealized) included in earnings	0.1	0.1
Net unrealized (losses) gains included in other comprehensive income	0.5	0.6
Purchases	2.8	8.5
Sales	(0.6)	(0.5)
Transfers in	0.0	1.0
Transfers out	(2.1)	(9.4)
Balance, end of period	13.5	12.8
Other assets
Changes in balance sheet carrying value associated with Level 3 financial assets carried at fair value
Balance, beginning of period	0.0	0.1
Total gains (losses) (realized/ unrealized) included in earnings		0.1
Net unrealized (losses) gains included in other comprehensive income		0.0
Purchases		0.0
Sales		0.0
Transfers in		0.0
Transfers out		0.0
Balance, end of period		0.0
Asset-backed
Changes in balance sheet carrying value associated with Level 3 financial assets carried at fair value
Balance, beginning of period	0.0	0.0
Total gains (losses) (realized/ unrealized) included in earnings	0.0	0.0
Net unrealized (losses) gains included in other comprehensive income	0.1	0.0
Purchases	2.0	8.5
Sales	0.0	0.0
Transfers in	0.0	0.0
Transfers out	(2.1)	(8.5)
Balance, end of period	0.0	0.0
Commercial mortgage-backed
Changes in balance sheet carrying value associated with Level 3 financial assets carried at fair value
Balance, beginning of period	3.5	3.3
Total gains (losses) (realized/ unrealized) included in earnings	0.1	0.0
Net unrealized (losses) gains included in other comprehensive income	0.4	0.2
Purchases	0.0	0.0
Sales	0.0	0.0
Transfers in	0.0	0.0
Transfers out	0.0	0.0
Balance, end of period	4.0	3.5
U.S. corporate
Changes in balance sheet carrying value associated with Level 3 financial assets carried at fair value
Balance, beginning of period	0.1	0.0
Total gains (losses) (realized/ unrealized) included in earnings	0.0	0.0
Net unrealized (losses) gains included in other comprehensive income	0.0	0.0
Purchases	0.8	0.0
Sales	0.0	0.0
Transfers in	0.0	1.0
Transfers out	0.0	(0.9)
Balance, end of period	0.9	0.1
Foreign corporate
Changes in balance sheet carrying value associated with Level 3 financial assets carried at fair value
Balance, beginning of period	8.1	8.2
Total gains (losses) (realized/ unrealized) included in earnings	0.0	0.0
Net unrealized (losses) gains included in other comprehensive income	0.1	0.4
Purchases	0.0	0.0
Sales	(0.6)	(0.5)
Transfers in	0.0	0.0
Transfers out	0.0	0.0
Balance, end of period	7.6	8.1
Non-redeemable preferred stocks
Changes in balance sheet carrying value associated with Level 3 financial assets carried at fair value
Balance, beginning of period	1.1	1.1
Total gains (losses) (realized/ unrealized) included in earnings	0.0	0.0
Net unrealized (losses) gains included in other comprehensive income	(0.1)	0.0
Purchases	0.0	0.0
Sales	0.0	0.0
Transfers in	0.0	0.0
Transfers out	0.0	0.0
Balance, end of period	$ 1.0	$ 1.1

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

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- Definition

Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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- Definition

Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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