Investments - Allowance for Credit Losses (Details) - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning of the Year	$ 7,500,000	$ 3,300,000
Additions for Securities for which No Previous Expected Credit Losses were Recognized	3,800,000	1,300,000
Reduction Due to Sales		300,000
End of the Period	9,100,000	4,600,000
Net Increase (Decrease) in Allowance on Securities for which Expected Credit Losses were Previously Recognized	1,300,000	500,000
Debt Securities, Available-for-sale, Allowance for Credit Loss, Writeoff	(3,500,000)	(200,000)
Foreign Governments
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning of the Year	0	300,000
Additions for Securities for which No Previous Expected Credit Losses were Recognized		0
Reduction Due to Sales		0
End of the Period	0	300,000
Net Increase (Decrease) in Allowance on Securities for which Expected Credit Losses were Previously Recognized		200,000
Debt Securities, Available-for-sale, Allowance for Credit Loss, Writeoff		(200,000)
Bonds and Notes
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning of the Year	7,500,000	3,000,000.0
Additions for Securities for which No Previous Expected Credit Losses were Recognized	3,800,000	1,300,000
Reduction Due to Sales		300,000
End of the Period	9,100,000	4,300,000
Net Increase (Decrease) in Allowance on Securities for which Expected Credit Losses were Previously Recognized	1,300,000	300,000
Debt Securities, Available-for-sale, Allowance for Credit Loss, Writeoff	$ (3,500,000)	$ 0