Loans - Impaired Commercial Loans Considered as TDR Loans (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Impaired commercial loans as TDR	$ 1,243	[1],[2],[3]	$ 1,434	[1],[2],[3]
Commercial Loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired commercial loans as TDR	361	[1],[3]	460	[1],[3]
Unpaid principal balance of impaired commercial loans	595		806
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Charge-off of impaired loan	57
Impaired commercial loans as TDR	297	[1],[3]	343	[1],[3]
Unpaid principal balance of impaired commercial loans	414		552
Commercial Loan [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Impaired [Line Items]
Impaired commercial loans as TDR	34	[1],[3]	86	[1],[3]
Unpaid principal balance of impaired commercial loans	86		157
Commercial Loan [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Unpaid principal balance of impaired commercial loans	18		18
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Impaired commercial loans as TDR	30	[1],[3]	31	[1],[3]
Unpaid principal balance of impaired commercial loans	$ 77		$ 79

[1] TDR Loans are considered to be impaired loans. For consumer loans, all such loans are considered impaired loans regardless of accrual status. For commercial loans, impaired loans include other loans in addition to TDRs which totaled $171 million and $237 million at March 31, 2013 and December 31, 2012, respectively.

[2] Includes balances of $416 million and $519 million at March 31, 2013 and December 31, 2012, respectively, which are classified as nonaccrual loans.

[3] The TDR Loan balances included in the table above reflect the current carrying amount of TDR Loans and includes all basis adjustments on the loan, such as unearned income, unamortized deferred fees and costs on originated loans, partial charge-offs and premiums or discounts on purchased loans. The following table reflects the unpaid principal balance of TDR Loans:March 31, 2013 December 31, 2012 (in millions)Commercial loans: Construction and other real estate$318 $398Business and corporate banking73 137Other commercial33 34Total commercial424 569Consumer loans: Residential mortgages1,029 1,118Credit cards13 14Total consumer1,042 1,132Total$1,466 $1,701