Loans - Trouble Debt Restructuring Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	$ 1,207	$ 1,412	$ 1,241	$ 1,375
Interest income recognized on TDR loans	11	13	36	37
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	231	497	279	453
Interest income recognized on TDR loans	2	5	9	12
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	202	405	233	362
Interest income recognized on TDR loans	2	4	9	9
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	29	39	24	49
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	0	25	13	13
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	0	28	9	29
Interest income recognized on TDR loans	0	1	0	3
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	976	915	962	922
Interest income recognized on TDR loans	9	8	27	25
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	949	884	935	889
Interest income recognized on TDR loans	9	8	26	23
Consumer Loans [Member] | Home Equity Line of Credit [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	19	20	19	21
Interest income recognized on TDR loans	0	0	1	1
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Modifications [Line Items]
Average balance of TDR loans	8	11	8	12
Interest income recognized on TDR loans	$ 0	$ 0	$ 0	$ 1