Loans and Allowance for Loan Losses - Information about Impaired Loans by Class (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Impaired loans	$ 620	$ 572
Allowance for impaired loans	69	69
Average balance	574	567
With Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	408	380
Unpaid principal balance	456	414
Without Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	212	192
Unpaid principal balance	248	229
Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	190	220
Allowance for impaired loans	18	46
Average balance	201	185
Commercial and Industrial [Member] | With Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	125	182
Unpaid principal balance	131	191
Commercial and Industrial [Member] | Without Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	65	38
Unpaid principal balance	66	40
Commercial mortgage [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	121	130
Allowance for impaired loans	2	2
Average balance	121	191
Commercial mortgage [Member] | With Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	17	27
Unpaid principal balance	21	39
Commercial mortgage [Member] | Without Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	104	103
Unpaid principal balance	127	124
Construction [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	39	66
Allowance for impaired loans		6
Average balance	52	56
Construction [Member] | With Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	4	26
Unpaid principal balance	4	29
Construction [Member] | Without Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	35	40
Unpaid principal balance	38	43
Commercial portfolio [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	350	416
Allowance for impaired loans	20	54
Average balance	374	432
Commercial portfolio [Member] | With Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	146	235
Unpaid principal balance	156	259
Commercial portfolio [Member] | Without Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	204	181
Unpaid principal balance	231	207
Residential mortgage [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	260	142
Allowance for impaired loans	48	14
Average balance	188	117
Residential mortgage [Member] | With Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	260	142
Unpaid principal balance	297	148
Home equity and other consumer loans [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	2	2
Allowance for impaired loans	1
Average balance	2	2
Home equity and other consumer loans [Member] | With Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	2	2
Unpaid principal balance	2	2
Consumer portfolio [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	262	144
Allowance for impaired loans	49	14
Average balance	190	119
Consumer portfolio [Member] | With Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	262	144
Unpaid principal balance	299	150
Nonaccrual loans excluding FDIC covered loans [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	612	560
Allowance for impaired loans	69	68
Average balance	564	551
Nonaccrual loans excluding FDIC covered loans [Member] | With Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	408	379
Unpaid principal balance	455	409
Nonaccrual loans excluding FDIC covered loans [Member] | Without Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	204	181
Unpaid principal balance	231	207
FDIC covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	8	12
Allowance for impaired loans		1
Average balance	10	16
FDIC covered Loans [Member] | With Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans		1
Unpaid principal balance	1	5
FDIC covered Loans [Member] | Without Allowance [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans	8	11
Unpaid principal balance	$ 17	$ 22