Shareholders' Equity - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Oct. 28, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Preferred stock, shares authorized		1,000,000		1,000,000
Preferred stock, par value		$ 1.00		$ 1.00
Series F Fixed-to-Floating Non-cumulative Perpetual Preferred Stock [Member] | Subsequent Event
Class of Stock [Line Items]
Preferred stock, par value			$ 1.00
Preferred stock, shares issued			50,000
Preferred Stock, Liquidation Preference, Value			$ 10,000
Series D Fixed Rate Non-cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued		50,000		50,000
Preferred stock dividend rate		6.875%
Preferred stock, liquidation preference per share		$ 10,000		$ 10,000
Series D Fixed Rate Non-cumulative Perpetual Preferred Stock [Member] | Subsequent Event
Class of Stock [Line Items]
Stock expects to be redeemed	50,000
Preferred stock, liquidation preference per share	$ 10,000
Scenario Forecast | Series F Fixed-to-Floating Non-cumulative Perpetual Preferred Stock [Member] | Subsequent Event
Class of Stock [Line Items]
Preferred stock dividend rate	5.125%
Receivable dividends rate	3.52%
Date of change in the dividend rate	Nov. 01, 2026
Preferred Stock, Redemption Feature, Redemption Term	90 days
Warrant [Member] | Assumed In Acquisition [Member]
Class of Stock [Line Items]
Exercise price of each class of warrants or rights outstanding		$ 518.96		$ 518.96
Warrant to purchase common stock		95,383		95,383