Loans - Impaired Commercial Loans Considered as TDR Loans - Additional Information (Detail) - USD ($) $ in Millions		Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
TDR Loans	[1],[2],[3]	$ 1,249	$ 1,208
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	[2],[3]	201	210
Unpaid principal balance of impaired commercial loans		296	354
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	[2],[3]	120	186
Unpaid principal balance of impaired commercial loans		156	224
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	[2],[3]	68	24
Unpaid principal balance of impaired commercial loans		120	122
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	[2],[3]	13	0
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 $471 million and $485 million at June 30, 2015 and December 31, 2014, 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 $39 million and $85 million at June 30, 2015 and December 31, 2014, respectively.

[3] The TDR Loan balances included in the table above reflect the current carrying amount of TDR Loans and includes 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:June 30, 2015 December 31, 2014 (in millions)Commercial loans: Construction and other real estate$139 $201Business and corporate banking75 51Global banking13 —Total commercial227 252Consumer loans: Residential mortgages1,189 1,139 Home equity mortgages46 44Credit cards6 6Total consumer1,241 1,189Total$1,468 $1,441