VIE (Variable Interest Entities - Additional Information) (Detail) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2016
Variable Interest Entity
OTTI	[1]	$ 10	$ 3
Variable Interest Entity, Primary Beneficiary | Automobile Loans
Variable Interest Entity
Carry Value Of Loans Leases Or Lines Of Credit Securitized				$ 4,500
Variable Interest Entity, Primary Beneficiary | Fifth Third Community Development Corporation Investments
Variable Interest Entity
Maximum Exposure		32			$ 31
Variable Interest Entity, Not Primary Beneficiary | Loans Provided to VIEs
Variable Interest Entity
Unfunded commitment amounts		1,000			937
Variable Interest Entity, Not Primary Beneficiary | Fifth Third Community Development Corporation Investments
Variable Interest Entity
Maximum Exposure		1,424			1,421
Bancorp's Investment in Affordable Housing Tax Credits		1,424			1,421
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
Unfunded commitments		$ 356			349
Unfunded commitments expected funding date		2034
Variable Interest Entity, Not Primary Beneficiary | Private Equity Investments
Variable Interest Entity
Maximum Exposure		$ 178			232
Bancorp's Investment in Affordable Housing Tax Credits		121			176
Unfunded commitment amounts		57			$ 56
Capital Contribution To Private Equity Investments		6	2
OTTI		$ 0	$ 0

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