Variable Interest Entities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended	3 Months Ended
	Dec. 31, 2014	Mar. 31, 2013	Mar. 31, 2015	Mar. 31, 2014
Variable Interest Entity, Primary Beneficiary | Automobile Loan Securitizations
Variable Interest Entity [Line Items]
Carry Value Of Loans Leases Or Lines Of Credit Securitized	$ 3,800
Variable Interest Entity, Primary Beneficiary | Fifth Third Community Development Corporation Investments
Variable Interest Entity [Line Items]
Maximum Exposure	24		25
Variable Interest Entity, Not Primary Beneficiary | Loans Receivable
Variable Interest Entity [Line Items]
Unfunded commitment amounts	859		957
Variable Interest Entity, Not Primary Beneficiary | Automobile Loan Securitizations
Variable Interest Entity [Line Items]
Carry Value Of Loans Leases Or Lines Of Credit Securitized		509
Maximum Exposure	2		1
Total Assets	2		1
Variable Interest Entity, Not Primary Beneficiary | Fifth Third Community Development Corporation Investments
Variable Interest Entity [Line Items]
Maximum Exposure	1,432		1,402
Total Assets	1,432		1,402
Variable Interest Entity, Not Primary Beneficiary | Fifth Third Community Development Corporation Investments | Qualified Affordable Housing Tax Credits
Variable Interest Entity [Line Items]
Total Assets	1,300		1,200
Unfunded commitments	357		331
Unfunded commitments expected funding date			2031
Variable Interest Entity, Not Primary Beneficiary | Private Equity Funds
Variable Interest Entity [Line Items]
Maximum Exposure	267		262
Total Assets	189		194
Unfunded commitment amounts	78		68
Capital Contribution To Private Equity Funds			$ 10	$ 7