Dividend Restrictions (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Oct. 31, 2021	May 31, 2021	Jan. 01, 2021
NEW HAMPSHIRE [Member]
Statutory Accounting Practices [Line Items]
Percentage of policyholder's surplus distributes as dividends and other distributions		10.00%
Dividends declared	$ 245,000,000.0	$ 245,000,000.0	$ 140,000,000.0	$ 140,000,000.0
Dividends paid to parent		$ 245,000,000.0	140,000,000.0	140,000,000.0
NEW HAMPSHIRE [Member] | Scenario Forecast [Member]
Statutory Accounting Practices [Line Items]
Statutory amount available for dividend payments						$ 258,300,000
NEW HAMPSHIRE [Member] | Maximum [Member] | Scenario Forecast [Member]
Statutory Accounting Practices [Line Items]
Maximum dividends payable without prior approval of state regulators						$ 245,000,000.0
NEW HAMPSHIRE [Member] | Maximum [Member] | Subsequent Event [Member]
Statutory Accounting Practices [Line Items]
Maximum dividends payable without prior approval of state regulators							$ 13,300,000
MICHIGAN [Member]
Statutory Accounting Practices [Line Items]
Percentage of policyholder's surplus distributes as dividends and other distributions		10.00%
Dividends declared			106,000,000.0	87,900,000
Dividends paid to parent			$ 106,000,000.0	$ 87,900,000
Extraordinary dividends declared	82,000,000.0	$ 82,000,000.0
Extraordinary dividends paid to parent	$ 82,000,000.0
MICHIGAN [Member] | Scenario Forecast [Member]
Statutory Accounting Practices [Line Items]
Statutory amount available for dividend payments					$ 108,700,000
MICHIGAN [Member] | Maximum [Member] | Scenario Forecast [Member]
Statutory Accounting Practices [Line Items]
Maximum dividends payable without prior approval of state regulators					$ 82,000,000.0
MICHIGAN [Member] | Maximum [Member] | Subsequent Event [Member]
Statutory Accounting Practices [Line Items]
Maximum dividends payable without prior approval of state regulators							$ 26,700,000