Loans and Allowance for Loan Losses - Aging of Balance of Loans Held for Investment, Excluding FDIC Covered Loans (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 54,328	$ 51,913
30 to 89 Days Past Due	334	382
90 Days or More Past Due	224	296
Total Past Due	558	678
Total	54,886	52,591
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	21,015	20,033
30 to 89 Days Past Due	68	121
90 Days or More Past Due	3	37
Total Past Due	71	158
Total	21,086	20,191
Commercial mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	8,255	8,111
30 to 89 Days Past Due	32	49
90 Days or More Past Due	6	15
Total Past Due	38	64
Total	8,293	8,175
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	678	855
90 Days or More Past Due		15
Total Past Due		15
Total	678	870
Commercial portfolio [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	29,948	28,999
30 to 89 Days Past Due	100	170
90 Days or More Past Due	9	67
Total Past Due	109	237
Total	30,057	29,236
Residential mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	20,952	19,228
30 to 89 Days Past Due	187	188
90 Days or More Past Due	196	209
Total Past Due	383	397
Total	21,335	19,625
Home equity and other consumer loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,428	3,686
30 to 89 Days Past Due	47	24
90 Days or More Past Due	19	20
Total Past Due	66	44
Total	3,494	3,730
Consumer portfolio [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	24,380	22,914
30 to 89 Days Past Due	234	212
90 Days or More Past Due	215	229
Total Past Due	449	441
Total	$ 24,829	$ 23,355