Loans and Allowance for Loan Losses - Aging of Balance of Loans Held for Investment, Excluding Purchased Credit-Impaired Loans (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 63,792	$ 58,287
30 to 89 Days Past Due	378	355
90 Days or More Past Due	187	207
Total Past Due	565	562
Total loans held for investment, before purchased credit-impaired loans	64,357	58,849
Commercial and industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	23,169	21,861
30 to 89 Days Past Due	66	68
90 Days or More Past Due	15	2
Total Past Due	81	70
Total loans held for investment, before purchased credit-impaired loans	23,250	21,931
Commercial mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	12,851	9,869
30 to 89 Days Past Due	136	57
90 Days or More Past Due	21	13
Total Past Due	157	70
Total loans held for investment, before purchased credit-impaired loans	13,008	9,939
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	808	622
30 to 89 Days Past Due		5
Total Past Due		5
Total loans held for investment, before purchased credit-impaired loans	808	627
Commercial portfolio [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	36,828	32,352
30 to 89 Days Past Due	202	130
90 Days or More Past Due	36	15
Total Past Due	238	145
Total loans held for investment, before purchased credit-impaired loans	37,066	32,497
Residential mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	23,548	22,351
30 to 89 Days Past Due	152	181
90 Days or More Past Due	135	173
Total Past Due	287	354
Total loans held for investment, before purchased credit-impaired loans	23,835	22,705
Home equity and other consumer loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,416	3,584
30 to 89 Days Past Due	24	44
90 Days or More Past Due	16	19
Total Past Due	40	63
Total loans held for investment, before purchased credit-impaired loans	3,456	3,647
Consumer portfolio [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	26,964	25,935
30 to 89 Days Past Due	176	225
90 Days or More Past Due	151	192
Total Past Due	327	417
Total loans held for investment, before purchased credit-impaired loans	$ 27,291	$ 26,352