Shareholders' Equity - Issued and Outstanding Preferred Stock (Parenthetical) (Detail) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock, liquidation preference per share	$ 1,000	$ 1,000
Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock, liquidation preference per share	1,000	1,000
Series E Fixed-To-Floating Rate Non-Cumulative Perpetual Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock, liquidation preference per share	$ 1,000	$ 1,000
Preferred stock dividend rate	6.45%	6.45%
Date of change in the dividend rate	Feb. 14, 2024	Feb. 14, 2024
London Interbank offered rate plus basis points	3.61%	3.61%
Preferred shares redemption date	Feb. 15, 2024	Feb. 15, 2024
Preferred Stock, Redemption Feature, Redemption Term	90 days	90 days
Series F Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock, liquidation preference per share	$ 10,000	$ 10,000
Preferred stock dividend rate	5.125%	5.125%
Date of change in the dividend rate	Oct. 31, 2026	Oct. 31, 2026
London Interbank offered rate plus basis points	3.52%	3.52%
Preferred shares redemption date	Nov. 01, 2026	Nov. 01, 2026
Preferred Stock, Redemption Feature, Redemption Term	90 days	90 days
Series G Fixed-Rate Reset Non-cumulative Perpetual Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock, liquidation preference per share	$ 10,000	$ 10,000
Preferred stock dividend rate	5.00%	5.00%
Date of change in the dividend rate	Jul. 31, 2024	Jul. 31, 2024
Preferred shares redemption date	Aug. 01, 2024	Aug. 01, 2024
Preferred Stock, Redemption Feature, Redemption Term	90 days	90 days
U S treasury rate plus additional rate	3.174%	3.174%
Dividend payment terms	five-year	five-year