Loans - Average Balance and Interest Income Recognized on Impaired Commercial Loans (Detail) - Commercial Loans [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	$ 832	$ 278	$ 705	$ 283
Total interest income recognized on impaired commercial loans	5	1	8	3
Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	101	166	104	176
Total interest income recognized on impaired commercial loans	0	1	1	2
Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	427	92	382	91
Total interest income recognized on impaired commercial loans	3	0	5	1
Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	296	13	212	9
Total interest income recognized on impaired commercial loans	2	0	2	0
Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	$ 8	$ 7	$ 7	$ 7