Retirement and Benefit Plans (Retirement and Benefit Plans - Additional Information) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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		$ (7)
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 2018		17
Defined Benefit Plan Expected Future Benefit Payments in 2019		17
Defined Benefit Plan Expected Future Benefit Payments in 2020		17
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 through 2027		77
Estimated future defined benefit plan contributions		3
Plan assets managed	[1]	185	$ 172
Net underfunded status		(24)	(34)
Fifth Third Bank
Defined Benefit Plan Disclosure
Plan assets managed through collective funds		185	172
Non-qualified defined contribution plan
Defined Benefit Plan Disclosure
Expenses recognized for the Bancorp's defined contribution plan		4	3	$ 3
Qualified defined contribution plan
Defined Benefit Plan Disclosure
Expenses recognized for the Bancorp's defined contribution plan		79	75	71
Deferred profit sharing
Defined Benefit Plan Disclosure
Expenses recognized for the Bancorp's defined contribution plan		0	0	$ 0
Common stock | Fifth Third Bank
Defined Benefit Plan Disclosure
Plan assets managed		$ 0	$ 5

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