Loans - Impaired Commercial Loans Considered as TDR Loans (Detail) - Commercial Loans [Member] - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	$ 61	$ 92
Amount without Impairment Reserves	[1]	271	203
Total Impaired Commercial Loans	[1],[2]	332	295
Impairment Reserve		15	30
Unpaid principal balance of impaired commercial loans		390	354
Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	2	18
Amount without Impairment Reserves	[1]	114	179
Total Impaired Commercial Loans	[1],[2]	116	197
Impairment Reserve		1	5
Unpaid principal balance of impaired commercial loans		136	224
Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	59	72
Amount without Impairment Reserves	[1]	130	18
Total Impaired Commercial Loans	[1],[2]	189	90
Impairment Reserve		14	24
Unpaid principal balance of impaired commercial loans		226	122
Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	0	0
Amount without Impairment Reserves	[1]	21	0
Total Impaired Commercial Loans	[1],[2]	21	0
Impairment Reserve		0	0
Unpaid principal balance of impaired commercial loans		22	0
Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	0	2
Amount without Impairment Reserves	[1]	6	6
Total Impaired Commercial Loans	[1],[2]	6	8
Impairment Reserve		0	1
Unpaid principal balance of impaired commercial loans		$ 6	$ 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 $270 million and $210 million at September 30, 2015 and December 31, 2014, respectively.