VIE (Variable Interest Entities - Additional Information) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Variable Interest Entity
OTTI	[1]	$ 2	$ 0	$ 8	$ 5
Variable Interest Entity, Primary Beneficiary | Automobile Loans
Variable Interest Entity
Carry Value Of Loans Leases Or Lines Of Credit Securitized						$ 750	$ 3,800
Variable Interest Entity, Primary Beneficiary | Fifth Third Community Development Corporation Investments
Variable Interest Entity
Maximum Exposure		30		30		27
Variable Interest Entity, Not Primary Beneficiary | Loans Provided to VIEs
Variable Interest Entity
Unfunded commitment amounts		877		877		969
Variable Interest Entity, Not Primary Beneficiary | Fifth Third Community Development Corporation Investments
Variable Interest Entity
Maximum Exposure		1,409		1,409		1,455
Bancorp's Investment in Affordable Housing Tax Credits		1,409		1,409		1,455
Variable Interest Entity, Not Primary Beneficiary | Fifth Third Community Development Corporation Investments | Qualified Affordable Housing Tax Credits
Variable Interest Entity
Bancorp's Investment in Affordable Housing Tax Credits		1,300		1,300		1,300
Unfunded commitments		$ 329		329		356
Unfunded commitments expected funding date		2033
Variable Interest Entity, Not Primary Beneficiary | Private Equity Investments
Variable Interest Entity
Maximum Exposure		$ 247		247		271
Bancorp's Investment in Affordable Housing Tax Credits		186		186		211
Unfunded commitment amounts		61		61		$ 60
Capital Contribution To Private Equity Investments			6	8	28
OTTI		$ 9	$ 0	$ 9	$ 0

[1] (a) Included in securities gains, net, in the Condensed Consolidated Statements of Income.