Loans - Impaired Commercial Loans Considered as TDR Loans (Detail) - Commercial Loans [Member] - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	$ 419	$ 171
Amount without Impairment Reserves	[1]	294	282
Total Impaired Commercial Loans	[1],[2]	713	453
Impairment Reserve		257	54
Unpaid principal balance of impaired commercial loans		746	519
Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	4	2
Amount without Impairment Reserves	[1]	99	108
Total Impaired Commercial Loans	[1],[2]	103	110
Impairment Reserve		1	1
Unpaid principal balance of impaired commercial loans		115	125
Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	223	168
Amount without Impairment Reserves	[1]	130	124
Total Impaired Commercial Loans	[1],[2]	353	292
Impairment Reserve		83	52
Unpaid principal balance of impaired commercial loans		367	342
Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	191	0
Amount without Impairment Reserves	[1]	59	44
Total Impaired Commercial Loans	[1],[2]	250	44
Impairment Reserve		172	0
Unpaid principal balance of impaired commercial loans		257	44
Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	1	1
Amount without Impairment Reserves	[1]	6	6
Total Impaired Commercial Loans	[1],[2]	7	7
Impairment Reserve		1	1
Unpaid principal balance of impaired commercial loans		$ 7	$ 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 $444 million and $365 million at March 31, 2016 and December 31, 2015, respectivel