Shareholders' Equity - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Cash dividends declared on common shares, per share	$ 0.065	$ 0.055
2015 Capital Plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Repurchase of common stock	$ 725
Cash dividends declared on common shares, per share	$ 0.065
Cash dividends declared on common shares, per share	$ 0.075
2014 Capital Plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Repurchase of common stock	$ 208
2016 [Member] | 2015 Capital Plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Cash dividends declared on common shares, per share	$ 0.085