Loans - Loans Classified as TDR Loans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	$ 20	$ 16
Commercial Loan [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	12	2
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	12	2
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	8	14
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	8	13
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	$ 0	$ 1