Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Class of Stock
Total preferred stock value issued	$ 30.4	$ 30.4
$100 par value, Six Per Cent. Preferred Stock
Class of Stock
Par or stated value per share	$ 100	$ 100
Dividend rate (as a percentage)	6.00%	6.00%
Shares authorized	45,000	45,000
Shares outstanding	44,498	44,498
Redemption price per share	$ 0	$ 0
Total preferred stock value issued	$ 4.4	$ 4.4
$100 par value, Serial Preferred Stock, 3.60% Series
Class of Stock
Par or stated value per share	$ 100	$ 100
Dividend rate (as a percentage)	3.60%	3.60%
Shares authorized	2,286,500	2,286,500
Shares outstanding	260,000	260,000
Redemption price per share	$ 101	$ 101
Total preferred stock value issued	$ 26.0	$ 26.0
$25 par value, Serial Preferred Stock
Class of Stock
Par or stated value per share	$ 25	$ 25
Shares authorized	5,000,000	5,000,000
Shares outstanding	0	0
Redemption price per share	$ 0	$ 0
Total preferred stock value issued	$ 0.0	$ 0.0