Investments - Narrative, Cost or Amortized Cost, Gross Unrealized Gains and Losses, Fair Value and OTTI (Details) (Details) $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 46.7	$ 48.7
Cost or Amortized Cost	43.4	46.7
Fixed maturity securities available-for-sale, unrealized gains	3.3	$ 2.2
Total gross unrealized losses as a percentage of the aggregate fair value of the related securities		2.00%
Number of individual securities comprising total gross unrealized losses \| security		30
State, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Fair Value	3.2	$ 3.2
Cost or Amortized Cost	3.1	3.0
Fixed maturity securities available-for-sale, unrealized gains	0.1	0.2
Pre-refunded bonds \| State, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 1.5	$ 1.5
Municipal revenue bonds \| Credit concentration \| Investment portfolio \| State, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Concentration percentage	84.00%	83.00%
Fixed maturity securities
Debt Securities, Available-for-sale [Line Items]
Fixed maturity securities on deposit with various governmental authorities	$ 0.9	$ 0.9
Individual U. S. states \| Credit concentration \| Investment portfolio \| State, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Concentration percentage	3.00%	3.00%
Europe \| Corporate fixed maturity and equity securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	$ 6.0	$ 6.5
Fixed maturity securities available-for-sale, unrealized gains	$ 0.3	$ 0.1
Europe \| Credit concentration \| Investment portfolio \| Corporate fixed maturity and equity securities, financial sector
Debt Securities, Available-for-sale [Line Items]
Concentration percentage		11.00%
United Kingdom \| Credit concentration \| Investment portfolio \| Corporate fixed maturity and equity securities
Debt Securities, Available-for-sale [Line Items]
Concentration percentage	11.00%	15.00%

Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Losses, Before Taxes, Percentage

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- Definition

Carrying amount of cash and investment securities on deposit with state regulatory authorities in connection with capital requirements.

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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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).

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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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 unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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