Capital Actions - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2015	Dec. 31, 2014
Capital Actions [Line Items]
Issuance of preferred shares	$ 297
4.90% fixed-to-floating non-cumulative Series J perpetual preferred stock
Capital Actions [Line Items]
Preferred stock, issued		12,000	12,000
Preferred stock, liquidation preference		$ 25,000	$ 25,000