Loans - Impaired Commercial Loans Considered as TDR Loans (Detail) (Commercial Loan [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	$ 175		$ 250
Amount without Impairment Reserves	427		447
Total Impaired Commercial Loans	602	[1],[2],[3]	697	[1],[2],[3]
Impairment Reserve	58		96
Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	71		192
Amount without Impairment Reserves	349		305
Total Impaired Commercial Loans	420	[1],[2],[3]	497	[1],[2],[3]
Impairment Reserve	17		86
Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	39		57
Amount without Impairment Reserves	17		49
Total Impaired Commercial Loans	56	[1],[2],[3]	106	[1],[2],[3]
Impairment Reserve	32		10
Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	65		0
Amount without Impairment Reserves	0		18
Total Impaired Commercial Loans	65	[1],[2],[3]	18	[1],[2],[3]
Impairment Reserve	9		0
Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	0		1
Amount without Impairment Reserves	61		75
Total Impaired Commercial Loans	61	[1],[2],[3]	76	[1],[2],[3]
Impairment Reserve	$ 0		$ 0

[1] The impaired commercial loan balances included in the table above reflect the current carrying amount of the loan and includes all basis adjustments, such as partial charge-offs, unamortized deferred fees and costs on originated loans and any premiums or discounts. The following table reflects the unpaid principal balance of impaired commercial loans included in the table above: September 30, 2013 December 31, 2012 (in millions)Construction and other real estate$438 $552Business and corporate banking94 157Global banking65 18Other commercial64 79Total$661 $806

[2] The decrease in construction and other real estate impaired loans with impairment allowances since December 31, 2012 largely reflects the partial charge-off of a loan with a balance of $71 million and other decreases in previously impaired loans which was partially offset by the addition of currently performing TDR loans added in the second quarter of 2013 totaling $152 million, for which an insignificant amount of impairment reserves were required.

[3] Includes impaired commercial loans which are also considered TDR Loans as follows: September 30, 2013 December 31, 2012 (in millions)Construction and other real estate$375 $343Business and corporate banking51 86Global banking51 Other commercial27 31Total$504 $460