Shareholders' Equity - Issued and Outstanding Preferred Stock (Parenthetical) (Detail) (USD $)	12 Months Ended		1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Series D Fixed Rate Non-Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Liquidation preference	$ 10,000	10,000
Preferred stock dividend rate	6.875%
Preferred Stock, Redemption Feature, Redemption Term	90 days
Preferred shares redemption date	Jun. 15, 2016
Series E Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Liquidation preference	$ 1,000	1,000
Preferred stock dividend rate	6.45%
Date of change in the dividend rate	Feb. 14, 2024
Preferred Stock, Redemption Feature, Redemption Term	90 days
Preferred shares redemption date	Feb. 15, 2024
London Interbank offered rate plus basis points	3.61%
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Liquidation preference	$ 1,000	1,000
Exercise of warrants into shares of common stock	1,218,522
Exercise price of each class of warrants or rights outstanding	$ 73.86
Date of change in the dividend rate	Nov. 14, 2013
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member] | Dividend Paid Rate up to November 14, 2013 [Member]
Class of Stock [Line Items]
Preferred stock dividend rate	5.00%
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member] | Dividend Paid Rate Thereafter November 14, 2013 [Member]
Class of Stock [Line Items]
Preferred stock dividend rate	6.375%
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member] | Warrant [Member]
Class of Stock [Line Items]
Warrants and rights outstanding	721,490
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member] | Warrant [Member] | Cash Less Exercise [Member]
Class of Stock [Line Items]
Exercise of warrants into shares of common stock	427,905	69,127
Issuance of common shares	169,543	25,427
Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Liquidation preference	$ 1,000	1,000
Exercise of warrants into shares of common stock	407,542
Exercise price of each class of warrants or rights outstanding	$ 55.76
Date of change in the dividend rate	Nov. 14, 2013
Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member] | Dividend Paid Rate up to November 14, 2013 [Member]
Class of Stock [Line Items]
Preferred stock dividend rate	5.00%
Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member] | Dividend Paid Rate Thereafter November 14, 2013 [Member]
Class of Stock [Line Items]
Preferred stock dividend rate	6.375%
Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member] | Warrant [Member]
Class of Stock [Line Items]
Issuance of common shares			186,589