Loans and Loans Held for Sale - Loans by Category (Parenthetical) (Detail) (USD $)	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Loans [Line Items]
Commercial, financial and agricultural	$ 21,979,000,000	$ 24,317,000,000	$ 21,979,000,000	$ 23,242,000,000
Purchased loans		176,000,000	231,000,000	217,000,000
Net loan charge-offs	45,000,000
Commercial Credit Card [Member]
Loans [Line Items]
Commercial, financial and agricultural	88,000,000	96,000,000	88,000,000	90,000,000
PCI Loans [Member]
Loans [Line Items]
Purchased loans		18,000,000	25,000,000	23,000,000
Segment, Discontinued Operations [Member] | Education Lending [Member]
Loans [Line Items]
Loans	$ 5,300,000,000	$ 4,700,000,000	$ 5,300,000,000	$ 5,200,000,000