Loans - Summary of TDR and Related Credit Loss Reserves for TDR Loans (Detail) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Carrying Value of TDR Loans	[1],[2],[3]	$ 1,453	$ 1,208
Unpaid Principal Balance of TDR Loans	[1],[2],[3]	1,678	1,441
Allowance for credit losses on TDR Loans	[4]	59	56
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Carrying Value of TDR Loans	[2],[3]	365	210
Unpaid Principal Balance of TDR Loans	[2],[3]	390	252
Allowance for credit losses on TDR Loans	[4]	24	9
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Carrying Value of TDR Loans	[2],[3]	94	186
Unpaid Principal Balance of TDR Loans	[2],[3]	106	201
Allowance for credit losses on TDR Loans	[4]	0	4
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Carrying Value of TDR Loans	[2],[3]	227	24
Unpaid Principal Balance of TDR Loans	[2],[3]	240	51
Allowance for credit losses on TDR Loans	[4]	24	5
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Carrying Value of TDR Loans	[2],[3]	44	0
Unpaid Principal Balance of TDR Loans	[2],[3]	44	0
Allowance for credit losses on TDR Loans	[4]	0	0
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Carrying Value of TDR Loans	[2],[3]	1,088	998
Unpaid Principal Balance of TDR Loans	[2],[3]	1,288	1,189
Allowance for credit losses on TDR Loans	[4]	35	47
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Carrying Value of TDR Loans	[2],[3],[5]	1,060	972
Unpaid Principal Balance of TDR Loans	[2],[3],[5]	1,233	1,139
Allowance for credit losses on TDR Loans	[4]	33	43
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Carrying Value of TDR Loans	[2],[3],[5]	23	20
Unpaid Principal Balance of TDR Loans	[2],[3],[5]	50	44
Allowance for credit losses on TDR Loans	[4]	1	2
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Impaired [Line Items]
Carrying Value of TDR Loans	[2],[3]	5	6
Unpaid Principal Balance of TDR Loans	[2],[3]	5	6
Allowance for credit losses on TDR Loans	[4]	$ 1	$ 2

[1] At December 31, 2015 and 2014, the carrying value reflected above includes $676 million and $485 million, 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 $88 million and $85 million at December 31, 2015 and 2014, respectively.

[3] The carrying value of TDR Loans includes basis adjustments on the loans, such as unearned income, unamortized deferred fees and costs on originated loans, partial charge-offs and premiums or discounts on purchased loans.

[4] Included in the allowance for credit losses.

[5] At December 31, 2015 and 2014, the carrying value reflected above includes $881 million and $763 million, respectively, of loans that are recorded at the lower of amortized cost or fair value of the collateral less cost to sell.