Loans and Allowance for Loan Losses - Summary of Loans (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Jun. 30, 2012	Dec. 31, 2011		Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010
Loans held for investment
Commercial and industrial	$ 20,124			$ 19,226
Commercial mortgage	8,293			8,175
Construction	678			870
Lease financing	962			965
Total commercial portfolio	30,057			29,236
Residential mortgage	21,335			19,625
Home equity and other consumer loans	3,494			3,730
Total consumer portfolio	24,829			23,355
Total	54,886			52,591
FDIC covered loans	524			949
Total loans held for investment	55,410	[1]		53,540	[1]
Allowance for loan losses	(668)		(656)	(764)		(768)	(826)	(1,191)
Loans held for investment, net	$ 54,742			$ 52,776

[1] Includes $6 million and ($30) million at September 30, 2012 and December 31, 2011, respectively, for net unamortized discounts and premiums and deferred fees and costs.