Loans - Summary of Past Due Status of Loans (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 1-29 days	$ 2,118	$ 1,882
Days Past Due, 30-89 days	609	760
Days Past Due, 90 + days	1,171	1,367
Total Past Due	3,898	4,009
Current	59,034	59,249
Total loans	62,932	63,258	53,869
Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 1-29 days	1,668	1,399
Days Past Due, 30-89 days	112	208
Days Past Due, 90 + days	131	261
Total Past Due	1,911	1,868
Current	41,728	42,282
Total loans	43,639	44,150
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 1-29 days	94	27
Days Past Due, 30-89 days	31	89
Days Past Due, 90 + days	62	152
Total Past Due	187	268
Current	8,132	8,189
Total loans	8,319	8,457	7,777
Commercial Loan [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 1-29 days	684	558
Days Past Due, 30-89 days	36	73
Days Past Due, 90 + days	42	70
Total Past Due	762	701
Current	11,963	11,907
Total loans	12,725	12,608	10,889
Commercial Loan [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 1-29 days	547	777
Days Past Due, 30-89 days	17	30
Days Past Due, 90 + days	8	8
Total Past Due	572	815
Current	19,146	19,194
Total loans	19,718	20,009	13,852
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 1-29 days	343	37
Days Past Due, 30-89 days	28	16
Days Past Due, 90 + days	19	31
Total Past Due	390	84
Current	2,487	2,992
Total loans	2,877	3,076	3,051
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 1-29 days	450	483
Days Past Due, 30-89 days	497	552
Days Past Due, 90 + days	1,040	1,106
Total Past Due	1,987	2,141
Current	17,306	16,967
Total loans	19,293	19,108
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 1-29 days	338	348
Days Past Due, 30-89 days	34	40
Days Past Due, 90 + days	69	82
Total Past Due	441	470
Current	1,795	1,854
Total loans	2,236	2,324	2,491
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 1-29 days	85	100
Days Past Due, 30-89 days	448	493
Days Past Due, 90 + days	931	976
Total Past Due	1,464	1,569
Current	14,266	13,802
Total loans	15,730	15,371	14,344
Consumer Loans [Member] | Credit Card Receivables [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 1-29 days	22	28
Days Past Due, 30-89 days	12	14
Days Past Due, 90 + days	13	15
Total Past Due	47	57
Current	702	758
Total loans	749	815	786
Consumer Loans [Member] | Consumer Other Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 1-29 days	5	7
Days Past Due, 30-89 days	3	5
Days Past Due, 90 + days	27	33
Total Past Due	35	45
Current	543	553
Total loans	$ 578	$ 598	$ 679