Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]

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Debt Securities, Available-for-sale, Unrealized Loss Position Abstract [Abstract]

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Fair value of positions with a gross unrealized loss as a percentage of total fixed maturities and equities fair value.

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Fair value of positions with a gross unrealized loss for twelve months or less as a percentage of total fixed maturities and equities fair value.

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Fair value of positions with a gross unrealized loss for more than twelve months as a percentage of total fixed maturities and equities fair value.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Investments - Gross Unrealized Losses of Fixed Maturities and Equity Securities in Unrealized Loss Position (Details) $ in Millions	Dec. 31, 2022 USD ($)	Dec. 31, 2022 security	Dec. 31, 2022	Dec. 31, 2022 position	Dec. 31, 2021 USD ($)	Dec. 31, 2021 security	Dec. 31, 2021	Dec. 31, 2021 position
Fixed maturity securities, Gross Unrealized Losses
Number of positions with a gross unrealized loss, 12 months or less \| security		2,515				516
Number of position with a gross unrealized loss, more than 12 months		587		587		122		122
Number of position with a gross unrealized loss, total \| security		3,102				638
Fair value as a percentage of total fixed maturities and equity securities fair value, 12 months or less			68.20%				12.60%
Fair value as a percentage of total fixed maturities and equity securities fair value, more than 12 months			14.20%				3.40%
Fair value as a percentage of total fixed maturities and equity securities fair value, total			82.40%				16.00%
Total
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair value, 12 months or less	$ 3,533.7				$ 783.4
Fixed maturity securities, fair value, more than 12 months	734.2				211.9
Fixed maturity securities, fair value, total	4,267.9				995.3
Fixed maturity securities, Gross Unrealized Losses
Fixed maturity securities, gross unrealized losses, 12 months or less	461.8				11.3
Fixed maturity securities, gross unrealized losses, more than 12 months	145.1				7.3
Fixed maturity securities, gross unrealized losses, total	606.9				18.6
Mortgage-backed securities
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair value, 12 months or less	458.3				67.4
Fixed maturity securities, fair value, more than 12 months	52.6				3.9
Fixed maturity securities, fair value, total	510.9				71.3
Fixed maturity securities, Gross Unrealized Losses
Fixed maturity securities, gross unrealized losses, 12 months or less	54.4				1.3
Fixed maturity securities, gross unrealized losses, more than 12 months	14.7				0.2
Fixed maturity securities, gross unrealized losses, total	69.1				1.5
Other
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair value, 12 months or less	242.7				59.5
Fixed maturity securities, fair value, more than 12 months	65.8				35.1
Fixed maturity securities, fair value, total	308.5				94.6
Fixed maturity securities, Gross Unrealized Losses
Fixed maturity securities, gross unrealized losses, 12 months or less	34.1				1.7
Fixed maturity securities, gross unrealized losses, more than 12 months	33.7				2.6
Fixed maturity securities, gross unrealized losses, total	67.8				4.3
Municipal bonds
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair value, 12 months or less	911.6				56.8
Fixed maturity securities, fair value, more than 12 months	42.2				0.6
Fixed maturity securities, fair value, total	953.8				57.4
Fixed maturity securities, Gross Unrealized Losses
Fixed maturity securities, gross unrealized losses, 12 months or less	113.7				0.7
Fixed maturity securities, gross unrealized losses, more than 12 months	14.4				0.0
Fixed maturity securities, gross unrealized losses, total	128.1				0.7
Foreign government bonds
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair value, 12 months or less	32.7				0.0
Fixed maturity securities, fair value, more than 12 months	0.4				0.0
Fixed maturity securities, fair value, total	33.1				0.0
Fixed maturity securities, Gross Unrealized Losses
Fixed maturity securities, gross unrealized losses, 12 months or less	1.4				0.0
Fixed maturity securities, gross unrealized losses, more than 12 months	0.2				0.0
Fixed maturity securities, gross unrealized losses, total	1.6				0.0
Corporate bonds
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair value, 12 months or less	1,345.0				220.7
Fixed maturity securities, fair value, more than 12 months	148.9				44.1
Fixed maturity securities, fair value, total	1,493.9				264.8
Fixed maturity securities, Gross Unrealized Losses
Fixed maturity securities, gross unrealized losses, 12 months or less	221.1				3.8
Fixed maturity securities, gross unrealized losses, more than 12 months	51.1				1.4
Fixed maturity securities, gross unrealized losses, total	272.2				5.2
Other asset-backed securities
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair value, 12 months or less	543.4				379.0
Fixed maturity securities, fair value, more than 12 months	424.3				128.2
Fixed maturity securities, fair value, total	967.7				507.2
Fixed maturity securities, Gross Unrealized Losses
Fixed maturity securities, gross unrealized losses, 12 months or less	37.1				3.8
Fixed maturity securities, gross unrealized losses, more than 12 months	31.0				3.1
Fixed maturity securities, gross unrealized losses, total	$ 68.1				$ 6.9