Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions					1 Months Ended	12 Months Ended
	Nov. 11, 2020	May 19, 2020	Feb. 21, 2019	Aug. 31, 2018	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Number of shares authorized to be repurchased						13,300,000
Purchase of treasury stock						$ 58.3	$ 215.4
Treasury stock acquired, Shares,						1,700,000	5,900,000
Treasury Stock Acquired, Average Cost Per Share						$ 33.35	$ 36.63
Common stock reissued						1,600,000	1,400,000
Preferred stock, dividend rate percentage	50.00%
Preferred stock, par value						$ 1	$ 1	$ 1.00
Non-Cumulative Perpetual Preferred Stock, Series B [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Issuance of preferred stock			$ 150.0
Preferred stock, dividend rate percentage			6.25%
Preferred stock, par value			$ 1.00
Preferred stock liquidation preference per depositary share			25
Preferred stock, liquidation preference per share			$ 25,000
Preferred stock, redemption terms						The Company may redeem the Series B preferred stock at its option, subject to regulatory approval, on or after March 15, 2024.
Non-Cumulative Perpetual Preferred Stock, Series C [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Issuance of preferred stock		$ 225.0
Preferred stock, dividend rate percentage		6.125%
Preferred stock, par value		$ 1.00
Preferred stock liquidation preference per depositary share		25
Preferred stock, liquidation preference per share		$ 25,000
Preferred stock, redemption terms						The Company may redeem the Series C preferred stock at its option, subject to regulatory approval, on or after June 15, 2025.
Series B Preferred Stock [Member] | Over-Allotment Option [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Issuance of preferred stock					$ 10.0
Series C Preferred Stock [Member] | Over-Allotment Option [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Issuance of preferred stock		$ 25.0
Business Bancshares, Inc. [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Stock issued for acquisition				2,000,000.0