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Option to purchase additiona Non-voting units of Vantiv Holding, LLC

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Valuation adjustments for loans held for sale and portfolio loans.

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Sensitivity Analysis of Decrease in Fair Value of Derivatives, Impact of 25 Basis Point Increase in the Interest Rate

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Sensitivity Analysis of Increase in Fair Value of Derivatives, Impact of 50 Basis Point Decrease in the Interest Rate

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Sensitivity Analysis of Increase in Fair Value of Derivatives, Impact of 10% Changes in the Assumed Loan Closing Rates

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Sensitivity Analysis of Increase in Fair Value of Derivatives, Impact of 25 Basis Point Decrease in the Interest Rate

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Sensitivity Analysis of Increase in Fair Value of Derivatives, Impact of 20% Changes in the Assumed Loan Closing Rates

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Amount of addition (reduction) to the amount at which an asset could be incurred (settled) in a current transaction between willing parties.

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Exercise price per share or per unit of warrants or rights outstanding.

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Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

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For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

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This item represents the estimated amount of gains or losses included in earnings during the period attributable to changes in instrument-specific credit risk arising from loans and other receivables held as assets.

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The net gain (loss) resulting from a sale of loans, including adjustments to record loans classified as held-for-sale at the lower-of-cost-or-market and fair value adjustments to loan held for investment purposes.

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The hypothetical financial impact of a 10 percent adverse change of the specified assumption on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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The hypothetical financial impact of a 20 percent adverse change of the specified assumption on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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Value of loans held-for-sale transferred to loans held in the entity's portfolio in noncash transactions.

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Value of loans and leases held in the entity's portfolio transferred to loans and leases held-for-sale in noncash transactions.

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Fair Value Measurements - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Jun. 30, 2009
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial loans transferred from the portfolio to loans held for sale	$ 9	$ 73
Existing loans held for sale, further adjusted	689		561
Residential loans transferred to the Bancorp's portfolio	78	12
Fair value changes included in earnings for instruments for which the fair value option was elected	30	23
Incremental Unit Purchase Option	20fitb_IncrementalUnitPurchaseOption
Vantiv Holding, LLC Warrant Exercise Price	$ 15.98
Percentage of Vantiv Holding, LLC sold to Advent for cash and warrants				51.00%
Residential Mortgage Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential loans transferred to the Bancorp's portfolio	55
Fair value adjustment	1
The fair value of loans	1		2
Interest Rate Lock Commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net fair value of the interest rate lock commitments	19
Change in the fair value of the interest rate lock commitments, due to decrease in current interest rates of 25 bp	7
Change in the fair value of the interest rate lock commitments, due to decrease in current interest rates of 50 bp	14
Change in the fair value of the interest rate lock commitments, due to increase in current interest rates of 25 bp	8
Change in the fair value of the interest rate lock commitments, due to increase in current interest rates of 50 bp	16
Change in fair value of interest rate lock commitments, due to 10% adverse changes in the assumed loan closing rates	2
Change in fair value of interest rate lock commitments, due to 20% adverse changes in the assumed loan closing rates	4
Change in fair value of interest rate lock commitments, due to 10% favorable changes in the assumed loan closing rates	2
Change in fair value of interest rate lock commitments, due to 20% favorable changes in the assumed loan closing rates	4
Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net impact related to fair value adjustments	3	10
Nonrecurring Losses Included As Charge-Offs	5	3
Commercial Loans Held For Sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net impact related to fair value adjustments	1	1
Gain Loss On Sales Of Loans Net	$ 5