Retirement and Benefit Plans (Retirement and Benefit Plans - Additional Information) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure
The estimated net actuarial loss for the defined benefit pension plans that will be amortized from accumulated other comprehensive income into net periodic benefit cost		$ 6
The increase in pension expense by lowering both the expected rate of return on the plan and the discount rate by 0.25%		1
Defined Benefit Plan Expected Future Benefit Payments in 2020		16
Defined Benefit Plan Expected Future Benefit Payments in 2021		17
Defined Benefit Plan Expected Future Benefit Payments in 2022		17
Defined Benefit Plan Expected Future Benefit Payments in 2023		17
Defined Benefit Plan Expected Future Benefit Payments in 2024		16
Defined Benefit Plan Expected Future Benefit Payments in 2025 through 2029		70
Estimated future defined benefit plan contributions		2
Plan assets	[1]	175	$ 164
Funded plan status			100.00%
Fifth Third Bank, National Association
Defined Benefit Plan Disclosure
Plan assets		164	$ 175
Deferred profit sharing
Defined Benefit Plan Disclosure
Expenses recognized for the Bancorp's defined contribution plan		0	0
Qualified defined contribution plan
Defined Benefit Plan Disclosure
Expenses recognized for the Bancorp's defined contribution plan		90	83	$ 79
Non-qualified defined contribution plan
Defined Benefit Plan Disclosure
Expenses recognized for the Bancorp's defined contribution plan		6	$ 4	$ 4
Deferred Profit Sharing [Member] | MB Financial, Inc.
Defined Benefit Plan Disclosure
Deferred Compensation Arrangement with Individual, Allocated Share-based Compensation Expense		$ 4

[1] For further information on fair value hierarchy levels, refer to Note 1.