Shareholders' Equity And Earnings Per Share (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended			3 Months Ended
	May 31, 2020	Jan. 31, 2020	Jun. 30, 2015	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2015
Temporary Equity [Line Items]
Cash dividends declared per common share (usd per share)		$ 0.31		$ 0.31	$ 0.28
Common stock dividends per share declared annualized (usd per share)		$ 1.24
Series D Preferred Stock
Temporary Equity [Line Items]
Sale of stock (in shares)			5,000,000
Preferred stock, liquidation value per share (usd per share)				25	25	$ 25	$ 25
Sale of stock, proceeds			$ 125.0
Preferred stock, dividend rate, percentage			6.50%
Series E Preferred Stock
Temporary Equity [Line Items]
Sale of stock (in shares)	11,500
Preferred stock, liquidation value per share (usd per share)	$ 25,000			$ 25,000	$ 25,000	$ 25,000
Preferred stock, dividend rate, percentage	6.875%
Depositary Shares
Temporary Equity [Line Items]
Sale of stock (in shares)	11,500,000
Sale of stock, proceeds	$ 287.5
London Interbank Offered Rate (LIBOR) | Series D Preferred Stock
Temporary Equity [Line Items]
Preferred stock, dividend rate, percentage, variable spread			4.06%