Loans and Loans Held for Sale - Loans by Category (Parenthetical) (Detail) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial, financial and agricultural	$ 31,095	$ 26,683	$ 27,982
Commercial lease financing includes receivables held as collateral for secured borrowing	162	367	302
Purchased loans	119	143	138
Education Lending [Member] | Discontinued Operations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,900	2,400	2,300
Commercial Credit Card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial, financial and agricultural	88	90	88
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased loans	$ 12	$ 14	$ 13