Loans and Allowance for Loan Losses - Reconciliation of Changes in Allowance for Loan Losses by Portfolio Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Commercial portfolio [Member]	Jun. 30, 2012 Commercial portfolio [Member]	Jun. 30, 2013 Commercial portfolio [Member]	Jun. 30, 2012 Commercial portfolio [Member]	Jun. 30, 2013 Consumer portfolio [Member]	Jun. 30, 2012 Consumer portfolio [Member]	Jun. 30, 2013 Consumer portfolio [Member]	Jun. 30, 2012 Consumer portfolio [Member]	Jun. 30, 2013 Purchased Credit Impaired [Member]	Jun. 30, 2012 Purchased Credit Impaired [Member]	Jun. 30, 2013 Purchased Credit Impaired [Member]	Jun. 30, 2012 Purchased Credit Impaired [Member]	Jun. 30, 2012 Unallocated portfolio [Member]	Jun. 30, 2013 Unallocated portfolio [Member]	Jun. 30, 2012 Unallocated portfolio [Member]	Mar. 31, 2013 Unallocated portfolio [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning of period	$ 638	$ 704	$ 653	$ 764	$ 486	$ 439	$ 418	$ 474	$ 113	$ 128	$ 124	$ 138	$ 1	$ 10	$ 1	$ 17	$ 127	$ 110	$ 135	$ 38
(Reversal of) provision for loan losses	(3)	(13)	(6)	(12)	(3)	(38)	65	(41)		14	1	26					11	(72)	3
(Reversal of) provision for FDIC covered loan losses not subject to FDIC indemnification		(1)		(3)										(1)		(3)
Decrease in allowance covered by FDIC indemnification	(2)	(3)		(9)									(2)	(3)		(9)
Loans charged off	(20)	(44)	(39)	(107)	(12)	(26)	(15)	(66)	(8)	(16)	(21)	(39)		(2)	(3)	(2)
Recoveries of loans previously charged off	12	13	17	23	9	13	12	21	1		2	1	2		3	1
Allowance for loan losses, end of period	$ 625	$ 656	$ 625	$ 656	$ 480	$ 388	$ 480	$ 388	$ 106	$ 126	$ 106	$ 126	$ 1	$ 4	$ 1	$ 4	$ 138	$ 38	$ 138	$ 38