Loans - Summary of TDR and Related Credit Loss Reserves for TDR Loans (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]
Allowance for credit losses on TDR Loans	51	[4]	56	[4]
Unpaid Principal Balance of TDR Loans	1,457		1,441
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	236	[2],[3]	210	[2],[3]
Allowance for credit losses on TDR Loans	6	[4]	9	[4]
Unpaid Principal Balance of TDR Loans	260		252
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	179	[2],[3]	186	[2],[3]
Allowance for credit losses on TDR Loans	2	[4]	4	[4]
Unpaid Principal Balance of TDR Loans	197		201
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	44	[2],[3]	24	[2],[3]
Allowance for credit losses on TDR Loans	4	[4]	5	[4]
Unpaid Principal Balance of TDR Loans	50		51
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	13	[2],[3]	0	[2],[3]
Unpaid Principal Balance of TDR Loans	13		0
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	1,006	[2],[3]	998	[2],[3]
Allowance for credit losses on TDR Loans	45	[4]	47	[4]
Unpaid Principal Balance of TDR Loans	1,197		1,189
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	980	[2],[3],[5]	972	[2],[3],[5]
Allowance for credit losses on TDR Loans	42	[4]	43	[4]
Unpaid Principal Balance of TDR Loans	1,147		1,139
Consumer Loans [Member] | Home Equity Line of Credit [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	20	[2],[3],[5]	20	[2],[3],[5]
Allowance for credit losses on TDR Loans	1	[4]	2	[4]
Unpaid Principal Balance of TDR Loans	44		44
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	6	[2],[3]	6	[2],[3]
Allowance for credit losses on TDR Loans	2	[4]	2	[4]
Unpaid Principal Balance of TDR Loans	$ 6		$ 6

[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.

[4] Included in the allowance for credit losses.

[5] Includes $778 million and $763 million at March 31, 2015 and December 31, 2014, respectively, of loans that are recorded at the lower of amortized cost or fair value of the collateral less cost to sell.