Loans - Trouble Debt Restructuring Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	$ 1,252	$ 1,300	$ 1,234
Interest income recognized on TDR loans	39	45	48
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	482	256	265
Interest income recognized on TDR loans	13	7	11
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	69	136	224
Interest income recognized on TDR loans	4	4	10
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	292	76	24
Interest income recognized on TDR loans	8	3	1
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	121	44	10
Interest income recognized on TDR loans	1	0	0
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	0	0	7
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	770	1,044	969
Interest income recognized on TDR loans	26	38	37
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	740	1,017	942
Interest income recognized on TDR loans	25	37	36
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	25	21	19
Interest income recognized on TDR loans	1	1	1
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	$ 5	$ 6	$ 8