Loans - Impaired Commercial Loans Considered as TDR Loans (Detail) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
TDR Loans	[1],[2],[3]	$ 1,222	$ 1,453
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[4]	596	171
Amount without Impairment Reserves	[4]	457	282
Total Impaired Commercial Loans	[4],[5]	1,053	453
Impairment Reserve		308	54
Unpaid principal balance of impaired commercial loans		1,123	519
TDR Loans	[2],[3],[6]	482	365
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[4]	2	2
Amount without Impairment Reserves	[4]	41	108
Total Impaired Commercial Loans	[4],[5]	43	110
Impairment Reserve		1	1
Unpaid principal balance of impaired commercial loans		45	125
TDR Loans	[2],[3]	32	94
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[4]	176	168
Amount without Impairment Reserves	[4]	166	49
Total Impaired Commercial Loans	[4],[5]	342	217
Impairment Reserve		55	52
Unpaid principal balance of impaired commercial loans		397	267
TDR Loans	[2],[3]	300	152
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[4]	417	0
Amount without Impairment Reserves	[4]	244	119
Total Impaired Commercial Loans	[4],[5]	661	119
Impairment Reserve		251	0
Unpaid principal balance of impaired commercial loans		674	119
TDR Loans	[2],[3]	150	119
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	$ 8

[1] At December 31, 2016 and 2015, the carrying value of TDR Loans includes $645 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 $571 million and $88 million at December 31, 2016 and 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 $482 million and $365 million at December 31, 2016 and 2015, respectively.

[6] Additional commitments to lend to commercial borrowers whose loans have been modified in TDR Loans totaled $184 million and $112 million at December 31, 2016 and 2015, respectively.