Loans - Trouble Debt Restructuring Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	$ 1,234	$ 1,374	$ 1,238
Interest income recognized on TDR loans	48	49	46
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	265	441	484
Interest income recognized on TDR loans	11	15	12
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	224	349	360
Interest income recognized on TDR loans	10	12	8
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	24	44	91
Interest income recognized on TDR loans	1	0	0
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	10	20	0
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	7	28	33
Interest income recognized on TDR loans	0	3	4
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	969	933	754
Interest income recognized on TDR loans	37	34	34
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	942	902	722
Interest income recognized on TDR loans	36	32	32
Consumer Loans [Member] | Home Equity Line of Credit [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	19	20	16
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	8	11	16
Interest income recognized on TDR loans	$ 0	$ 1	$ 1