Shareholders' Equity And Earnings Per Share (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended					3 Months Ended		9 Months Ended
	Jul. 31, 2020	May 31, 2020	Apr. 30, 2020	Jan. 31, 2020	Jun. 30, 2015	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Temporary Equity [Line Items]
Preferred stock, liquidation value per share (usd per share)						$ 25	$ 25	$ 25	$ 25	$ 25
Cash dividends declared per common share (usd per share)	$ 0.28		$ 0.28	$ 0.28		0.28	0.25	0.84	0.75
Common stock dividends per share declared annualized (usd per share)	$ 1.12		$ 1.12	$ 1.12
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	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	$ 0	$ 25,000	$ 0	$ 0
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%