Loans - Impaired Commercial Loans Considered as TDR Loans (Detail) - Commercial Loans [Member] - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	$ 171	$ 92
Amount without Impairment Reserves	[1]	282	203
Total Impaired Commercial Loans	[1],[2]	453	295
Impairment Reserve		54	30
Unpaid principal balance of impaired commercial loans		519	354
Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	2	18
Amount without Impairment Reserves	[1]	108	179
Total Impaired Commercial Loans	[1],[2]	110	197
Impairment Reserve		1	5
Unpaid principal balance of impaired commercial loans		125	224
Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	168	72
Amount without Impairment Reserves	[1]	124	18
Total Impaired Commercial Loans	[1],[2]	292	90
Impairment Reserve		52	24
Unpaid principal balance of impaired commercial loans		342	122
Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	0	0
Amount without Impairment Reserves	[1]	44	0
Total Impaired Commercial Loans	[1],[2]	44	0
Impairment Reserve		0	0
Unpaid principal balance of impaired commercial loans		44	0
Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	[1]	1	2
Amount without Impairment Reserves	[1]	6	6
Total Impaired Commercial Loans	[1],[2]	7	8
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 $365 million and $210 million at December 31, 2015 and 2014, respectively.