Goodwill and Core Deposit Intangibles - Goodwill Carrying Value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Goodwill [Roll Forward]
Net carrying value at beginning of period	$ 1,100.9	$ 621.6
Net carrying value at end of period	1,100.9	1,100.9
Goodwill, Acquired During Period	0.0	479.3
Goodwill	$ 1,100.9	$ 1,100.9