Loans - Impaired Commercial Loans Considered as TDR Loans (Detail) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
TDR Loans	[1],[2],[3]	$ 1,254	$ 1,453
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[4]	761	171
Amount without Impairment Reserves	[4]	374	282
Total Impaired Commercial Loans	[4],[5]	1,135	453
Impairment Reserve		342	54
Unpaid principal balance of impaired commercial loans		1,188	519
TDR Loans	[2],[3],[6]	521	365
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[4]	6	2
Amount without Impairment Reserves	[4]	53	108
Total Impaired Commercial Loans	[4],[5]	59	110
Impairment Reserve		2	1
Unpaid principal balance of impaired commercial loans		62	125
TDR Loans	[2],[3]	45	94
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[4]	204	168
Amount without Impairment Reserves	[4]	243	124
Total Impaired Commercial Loans	[4],[5]	447	292
Impairment Reserve		68	52
Unpaid principal balance of impaired commercial loans		482	342
TDR Loans	[2],[3]	404	227
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[4]	550	0
Amount without Impairment Reserves	[4]	72	44
Total Impaired Commercial Loans	[4],[5]	622	44
Impairment Reserve		271	0
Unpaid principal balance of impaired commercial loans		636	44
TDR Loans	[2],[3]	72	44
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[4]	1	1
Amount without Impairment Reserves	[4]	6	6
Total Impaired Commercial Loans	[4],[5]	7	7
Impairment Reserve		1	1
Unpaid principal balance of impaired commercial loans		$ 8	$ 8

[1] At September 30, 2016 and December 31, 2015, the carrying value of TDR Loans includes $610 million and $676 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 $614 million and $88 million at September 30, 2016 and December 31, 2015, 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] Reflects the carrying value of impaired commercial loans and includes basis adjustments on the loans, such as partial charge-offs, unamortized deferred fees and costs on originated loans and any premiums or discounts on purchased loans.

[5] Includes impaired commercial loans that are also considered TDR Loans which totaled $521 million and $365 million at September 30, 2016 and December 31, 2015, respectively.

[6] Additional commitments to lend to commercial borrowers whose loans have been modified in TDRs totaled $205 million and $112 million at September 30, 2016 and December 31, 2015, respectively.