Capital Structure - Schedule of Total Preferred Stock Outstanding (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	May 18, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		82,000	81,000
Proceeds from issuance of preferred stock, gross		$ 2,050.0	$ 2,025.0
Aggregate dividend payment		107.0	$ 105.0	$ 114.0
Excess redemption price over carrying value		$ 18.0
Series G (2)
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		0	23,000
Proceeds from issuance of preferred stock, gross		$ 0.0	$ 575.0
Dividend rate		5.625%
Dividends payable, amount per share (in usd per share)		$ 0.70	$ 1.41	$ 1.41
Aggregate dividend payment		$ 16.0	$ 32.0	$ 32.0
Series H
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		46,000	46,000
Proceeds from issuance of preferred stock, gross		$ 1,150.0	$ 1,150.0
Dividend rate		5.10%
Dividends payable, amount per share (in usd per share)		$ 1.28	$ 1.28	$ 1.28
Aggregate dividend payment		$ 59.0	$ 59.0	$ 59.0
Series I
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		12,000	12,000
Proceeds from issuance of preferred stock, gross		$ 300.0	$ 300.0
Dividend rate		4.75%
Dividends payable, amount per share (in usd per share)		$ 1.19	$ 1.19	$ 1.19
Aggregate dividend payment		$ 14.0	$ 14.0	$ 14.0
Series J
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)	24,000	24,000	0
Proceeds from issuance of preferred stock, gross	$ 600.0	$ 600.0	$ 0.0
Dividend rate		7.375%
Dividends payable, amount per share (in usd per share)		$ 0.75	$ 0	$ 0
Aggregate dividend payment		$ 18.0	$ 0.0	$ 0.0
National General Series
Class of Stock [Line Items]
Aggregate dividend payment		$ 0.0	$ 0.0	$ 9.0