Preferred Stock - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended		1 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jan. 31, 2012 Series A Preferred Stock Noncumulative Preferred Stock	Jan. 31, 2012 Series A Preferred Stock Noncumulative Preferred Stock Minimum	Jun. 30, 2012 Series B Preferred Stock Noncumulative Preferred Stock Fixed Rate	Jun. 30, 2012 Series B Preferred Stock Noncumulative Preferred Stock Minimum Fixed Rate
Class of Stock [Line Items]
Preferred stock, shares authorized	9,940,000	9,940,000
Preferred stock, par value	$ 0.01	$ 0.01
Depositary shares of non-cumulative perpetual preferred stock					19,400,000
Ownership interest percentage in a share of 6.00% non-cumulative perpetual preferred stock					2.50%
Value per depositary share					$ 25
Net proceeds from issuance of preferred stock offerings	$ 864		$ 394		$ 469
Fixed dividend rate on preferred stock			7.00%		6.00%
Preferred stock earliest redemption date				Feb. 01, 2022		Sep. 01, 2017
Fixed-to-floating rate non-cumulative perpetual preferred stock issued			400,000
End date of fixed dividend rate on Preferred stock			2022-02
Floating rate on 3-month LIBOR plus			4.82%