Allowance for Credit Losses - Summary of Changes in Allowance for Credit Losses and Related Loan Balance by Product (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 647		$ 743
Provision for credit losses	21	[1]	0	[1]
Charge-offs	(110)		(162)
Recoveries	10		22
Net charge offs	(100)		(140)
Balance at end of period	568		603
Ending balance: collectively evaluated for impairment	448		384
Ending balance: individually evaluated for impairment	120		219	[2]
Total allowances for credit losses	568		603
Collectively evaluated for impairment	60,598		51,581
Individually evaluated for impairment	782	[2]	1,530	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	1,552		758
Total loans	62,932		53,869		63,258
Commercial Loan [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans	43,639				44,150
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	162		212
Provision for credit losses	9		(20)
Charge-offs	(58)		(1)
Recoveries	3		14
Net charge offs	(55)		13
Balance at end of period	116		205
Ending balance: collectively evaluated for impairment	89		95
Ending balance: individually evaluated for impairment	27		110	[2]
Total allowances for credit losses	116		205
Collectively evaluated for impairment	7,926		7,122
Individually evaluated for impairment	393	[2]	655	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0
Total loans	8,319		7,777		8,457
Commercial Loan [Member] | Business Banking and Middle Markets Enterprises [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	97		78
Provision for credit losses	2		6
Charge-offs	(6)		(10)
Recoveries	3		2
Net charge offs	(3)		(8)
Balance at end of period	96		76
Ending balance: collectively evaluated for impairment	88		64
Ending balance: individually evaluated for impairment	8		12	[2]
Total allowances for credit losses	96		76
Collectively evaluated for impairment	12,678		10,750
Individually evaluated for impairment	47	[2]	139	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0
Total loans	12,725		10,889		12,608
Commercial Loan [Member] | Global Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	41		131
Provision for credit losses	(1)		(22)
Charge-offs	0		(84)
Recoveries	0		0
Net charge offs	0		(84)
Balance at end of period	40		25
Ending balance: collectively evaluated for impairment	40		25
Ending balance: individually evaluated for impairment	0		0	[2]
Total allowances for credit losses	40		25
Collectively evaluated for impairment	19,700		13,834
Individually evaluated for impairment	18	[2]	18	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0
Total loans	19,718		13,852		20,009
Commercial Loan [Member] | Other Commercial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	17		21
Provision for credit losses	0		(2)
Charge-offs	0		0
Recoveries	0		1
Net charge offs	0		1
Balance at end of period	17		20
Ending balance: collectively evaluated for impairment	17		20
Ending balance: individually evaluated for impairment	0		0	[2]
Total allowances for credit losses	17		20
Collectively evaluated for impairment	2,803		2,962
Individually evaluated for impairment	74	[2]	89	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0
Total loans	2,877		3,051		3,076
Consumer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period					114
Balance at end of period	106				114
Ending balance: individually evaluated for impairment	0
Total allowances for credit losses	106				114
Total loans	19,293				19,108
Consumer Loans [Member] | Residential Mortgage [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	210		192
Provision for credit losses	(3)		15
Charge-offs	(16)		(26)
Recoveries	1		1
Net charge offs	(15)		(25)
Balance at end of period	192		182
Ending balance: collectively evaluated for impairment	115		95
Ending balance: individually evaluated for impairment	77		87	[2]
Total allowances for credit losses	192		182
Collectively evaluated for impairment	13,962		12,990
Individually evaluated for impairment	216	[2]	596	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	1,552		758
Total loans	15,730		14,344		15,371
Consumer Loans [Member] | Home Equity Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	45		52
Provision for credit losses	17		8
Charge-offs	(12)		(17)
Recoveries	0		0
Net charge offs	(12)		(17)
Balance at end of period	50		43
Ending balance: collectively evaluated for impairment	47		39
Ending balance: individually evaluated for impairment	3		4	[2]
Total allowances for credit losses	50		43
Collectively evaluated for impairment	2,215		2,477
Individually evaluated for impairment	21	[2]	14	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0
Total loans	2,236		2,491		2,324
Consumer Loans [Member] | Credit Card [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	55		39
Provision for credit losses	(2)		11
Charge-offs	(12)		(17)
Recoveries	1		2
Net charge offs	(11)		(15)
Balance at end of period	42		35
Ending balance: collectively evaluated for impairment	37		29
Ending balance: individually evaluated for impairment	5		6	[2]
Total allowances for credit losses	42		35
Collectively evaluated for impairment	736		767
Individually evaluated for impairment	13	[2]	19	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0
Total loans	749		786		815
Consumer Loans [Member] | Other Consumer [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	20		18
Provision for credit losses	(1)		4
Charge-offs	(6)		(7)
Recoveries	2		2
Net charge offs	(4)		(5)
Balance at end of period	15		17
Ending balance: collectively evaluated for impairment	15		17
Ending balance: individually evaluated for impairment			0	[2]
Total allowances for credit losses	15		17
Collectively evaluated for impairment	578		679
Individually evaluated for impairment	0	[2]	0	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0
Total loans	$ 578		$ 679		$ 598

[1] The provision assigned to the segments is based on the segments’ net charge offs and the change in allowance for credit losses.

[2] (1) For consumer loans, these amounts represent TDR Loans for which we evaluate reserves using a discounted cash flow methodology. Each loan is individually identified as a TDR Loan and then grouped together with other TDR Loans with similar characteristics. The discounted cash flow analysis is then applied to these groups of TDR Loans. The loan balance above excludes TDR loans that are carried at the lower of amortized cost or fair value of the collateral less cost to sell which totaled $632 million and $445 million at March 31, 2013 and 2012, respectively.