Loans - Impaired Commercial Loans Considered as TDR Loans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
TDR Loans	$ 1,242	[1],[2],[3]	$ 1,208	[1],[2],[3]
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	236	[2],[3]	210	[2],[3]
Unpaid principal balance of impaired commercial loans	344		354
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	179	[2],[3]	186	[2],[3]
Unpaid principal balance of impaired commercial loans	223		224
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	44	[2],[3]	24	[2],[3]
Unpaid principal balance of impaired commercial loans	101		122
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	13	[2],[3]	0	[2],[3]
Unpaid principal balance of impaired commercial loans	13		0
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid principal balance of impaired commercial loans	$ 7		$ 8

[1] Includes $451 million and $485 million at March 31, 2015 and December 31, 2014, respectively, of loans which are classified as nonaccrual.

[2] 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, 2015 December 31, 2014 (in millions)Commercial loans: Construction and other real estate$197 $201Business and corporate banking50 51Global banking13 —Total commercial260 252Consumer loans: Residential mortgages1,147 1,139 Home equity mortgages44 44Credit cards6 6Total consumer1,197 1,189Total$1,457 $1,441

[3] 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 $79 million and $85 million at March 31, 2015 and December 31, 2014, respectively.