Loans - Impaired Commercial Loans Considered as TDR Loans (Detail) - Commercial Loans [Member] - USD ($) $ in Millions		Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	$ 852	$ 171
Amount without Impairment Reserves	[1]	398	282
Total Impaired Commercial Loans	[1],[2]	1,250	453
Impairment Reserve		353	54
Unpaid principal balance of impaired commercial loans		1,289	519
Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	6	2
Amount without Impairment Reserves	[1]	92	108
Total Impaired Commercial Loans	[1],[2]	98	110
Impairment Reserve		2	1
Unpaid principal balance of impaired commercial loans		110	125
Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	267	168
Amount without Impairment Reserves	[1]	234	124
Total Impaired Commercial Loans	[1],[2]	501	292
Impairment Reserve		103	52
Unpaid principal balance of impaired commercial loans		519	342
Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	578	0
Amount without Impairment Reserves	[1]	65	44
Total Impaired Commercial Loans	[1],[2]	643	44
Impairment Reserve		247	0
Unpaid principal balance of impaired commercial loans		652	44
Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	1	1
Amount without Impairment Reserves	[1]	7	6
Total Impaired Commercial Loans	[1],[2]	8	7
Impairment Reserve		1	1
Unpaid principal balance of impaired commercial loans		$ 8	$ 8

[1] ) 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

[2] ) Includes impaired commercial loans that are also considered TDR Loans which totaled $596 million and $365 million at June 30, 2016 and December 31, 2015, respectivel