Loans - Impaired Commercial Loans Considered as TDR Loans (Detail) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
TDR Loans	[1],[2],[3]	$ 1,134	$ 1,222
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[4]	607	596
Amount without Impairment Reserves	[4]	321	457
Total Impaired Commercial Loans	[4],[5]	928	1,053
Impairment Reserve		266	308
Unpaid principal balance of impaired commercial loans		1,009	1,123
TDR Loans	[2],[3],[6]	388	482
Commercial Loans [Member] | Real Estate, Including Construction [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[4]	33	2
Amount without Impairment Reserves	[4]	11	41
Total Impaired Commercial Loans	[4],[5]	44	43
Impairment Reserve		6	1
Unpaid principal balance of impaired commercial loans		46	45
TDR Loans	[2],[3]	31	32
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[4]	148	176
Amount without Impairment Reserves	[4]	176	166
Total Impaired Commercial Loans	[4],[5]	324	342
Impairment Reserve		36	55
Unpaid principal balance of impaired commercial loans		392	397
TDR Loans	[2],[3]	269	300
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[4]	425	417
Amount without Impairment Reserves	[4]	128	244
Total Impaired Commercial Loans	[4],[5]	553	661
Impairment Reserve		223	251
Unpaid principal balance of impaired commercial loans		564	674
TDR Loans	[2],[3]	88	150
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		$ 7	$ 7

[1] At March 31, 2017 and December 31, 2016, the carrying value of TDR Loans includes $515 million and $645 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 $540 million and $571 million at March 31, 2017 and December 31, 2016, 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 $388 million and $482 million at March 31, 2017 and December 31, 2016, respectively.

[6] Additional commitments to lend to commercial borrowers whose loans have been modified in TDR Loans totaled $232 million and $184 million at March 31, 2017 and December 31, 2016, respectively.