Shareholders' Equity - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended			3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Cash dividends declared on common shares, per share	$ 0.250	$ 0.215	$ 0.180
2014 Capital Plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Stock repurchase program authorized amount	$ 542			$ 542
Repurchase of common stock	355
Cash dividends declared on common shares, per share	$ 0.250			$ 0.065	$ 0.065	$ 0.065	$ 0.055
2013 Capital Plan[Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Repurchase of common stock	$ 496						$ 141