Variable Interest Entities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended									12 Months Ended				3 Months Ended		9 Months Ended
	Dec. 31, 2010 Variable Interest Entity, Primary Beneficiary Home Equity	Dec. 31, 2008 Variable Interest Entity, Primary Beneficiary Automobile Loan	Dec. 31, 2010 Variable Interest Entity, Primary Beneficiary Automobile Loan	Sep. 30, 2012 Variable Interest Entity, Primary Beneficiary Fifth Third Community Development Corporation Investments [Member]	Dec. 31, 2011 Variable Interest Entity, Primary Beneficiary Fifth Third Community Development Corporation Investments [Member]	Sep. 30, 2011 Variable Interest Entity, Primary Beneficiary Fifth Third Community Development Corporation Investments [Member]	Sep. 30, 2012 Variable Interest Entity, Not Primary Beneficiary Loans Receivable	Dec. 31, 2011 Variable Interest Entity, Not Primary Beneficiary Loans Receivable	Sep. 30, 2011 Variable Interest Entity, Not Primary Beneficiary Loans Receivable	Dec. 31, 2010 Variable Interest Entity, Not Primary Beneficiary Money Market Funds Upper Limit	Sep. 30, 2012 Variable Interest Entity, Not Primary Beneficiary Fifth Third Community Development Corporation Investments [Member]	Dec. 31, 2011 Variable Interest Entity, Not Primary Beneficiary Fifth Third Community Development Corporation Investments [Member]	Sep. 30, 2011 Variable Interest Entity, Not Primary Beneficiary Fifth Third Community Development Corporation Investments [Member]	Sep. 30, 2012 Variable Interest Entity, Not Primary Beneficiary Private Equity Funds	Sep. 30, 2011 Variable Interest Entity, Not Primary Beneficiary Private Equity Funds	Sep. 30, 2012 Variable Interest Entity, Not Primary Beneficiary Private Equity Funds	Sep. 30, 2011 Variable Interest Entity, Not Primary Beneficiary Private Equity Funds	Dec. 31, 2011 Variable Interest Entity, Not Primary Beneficiary Private Equity Funds	Sep. 30, 2012 Variable Interest Entity, Not Primary Beneficiary Restructured Loans	Dec. 31, 2011 Variable Interest Entity, Not Primary Beneficiary Restructured Loans	Sep. 30, 2011 Variable Interest Entity, Not Primary Beneficiary Restructured Loans
Variable Interest Entity [Line Items]
Carry Value Of Loans Leases Or Lines Of Credit Securitized	$ 903	$ 2,700
Number of seperate transactions in which the Bancorp previously sold loans to an isolated trust and conduits			3
Maximum Exposure				17	10	8					1,386	1,243	1,270	324	295	324	295	327	6	12	13
Unfunded commitment amounts							790	833	781					137	178	137	178	166		2	2
Capital Contribution To Private Equity Funds														11	14	35	29
Credit support										$ 1