Shareholders' Equity - Additional Information (Detail) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Class Of Stock [Line Items]
Preferred stock, shares authorized	1,000,000		1,000,000		1,000,000
Preferred stock, par value	$ 1.00		$ 1.00		$ 1.00
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared	15.9375	$ 15.9375	47.8125	$ 47.8125
Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared	15.9375	15.9375	47.8125	47.8125
Series E Fixed-To-Floating Rate Non-Cumulative Perpetual Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared	16.125	16.125	48.375	48.375
Series F Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 128.125	$ 128.125	$ 384.375	$ 384.375