Loans - Impaired Commercial Loans Considered as TDR Loans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
TDR Loans	$ 1,208	[1],[2],[3]	$ 1,370	[1],[2],[3]
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	210	[2],[3]	389	[2],[3]
Unpaid principal balance of impaired commercial loans	354		641
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	186	[2],[3]	292	[2],[3]
Unpaid principal balance of impaired commercial loans	224		380
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	24	[2],[3]	21	[2],[3]
Unpaid principal balance of impaired commercial loans	122		91
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	0	[2],[3]	51	[2],[3]
Unpaid principal balance of impaired commercial loans	0		123
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	0	[2],[3]	25	[2],[3]
Unpaid principal balance of impaired commercial loans	$ 8		$ 47

[1] Includes $485 million and $528 million at December 31, 2014 and 2013, respectively, of loans which are classified as nonaccrual.

[2] 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 TDR Loans which totaled $85 million and $92 million at December 31, 2014 and 2013, respectively.

[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:At December 31,2014 2013 (in millions)Commercial loans: Construction and other real estate$201 $309Business and corporate banking51 60Global banking— 51Other commercial— 28Total commercial252 448Consumer loans: Residential mortgages1,139 1,113 Home equity mortgages44 40Credit cards6 8Total consumer1,189 1,161Total$1,441 $1,609