Commitments (Commitments, Contingent Liabilities and Guarantees - Additional Information) (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017	Jun. 30, 2018	Dec. 31, 2017		Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2014	Sep. 30, 2012	Mar. 31, 2012	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010	Dec. 31, 2009
Loss Contingencies
Letters of credit	$ 2,062			$ 2,062				$ 2,185
Margin account balance held by the brokerage clearing agent	18			18				15
Amount in excess of amounts reserved	9			9
Credit loss reserve	1,091	[1]	$ 1,205	1,091	[1]	$ 1,205	$ 1,077	1,196	[1]	$ 1,226	$ 1,253
Residential Mortgage
Loss Contingencies
Amount in excess of amounts reserved	10			10
Outstanding balances on residential mortgage loans sold with representation and warranty provisions	6		10	6		10	7	9		$ 11	$ 13
Outstanding Repurchase Demand Inventory	5			5				1
Outstanding balances on residential mortgage loans sold with credit recourse	$ 282			$ 282				$ 312
Delinquency Rates	2.40%			2.40%				3.00%
Credit loss reserve	$ 5			$ 5				$ 5
Repurchased Outstanding Principal	4		4	11		9
Repurchase Demand Request	6		$ 4	17		$ 12
Secured Debt
Loss Contingencies
Fully and unconditionally guaranteed certain long-term borrowing obligations issued by wholly-owned issuing trust entities	62			62				62
Standby Letters of Credit
Loss Contingencies
Reserve for unfunded commitments	$ 5			$ 5				$ 6
Standby letters of credit as a percentage of total letters of credit	99.00%			99.00%				99.00%
Standby Letters of Credit | Secured Debt
Loss Contingencies
Standby letters of credit as a percentage of total letters of credit	61.00%			61.00%				61.00%
Variable Rate Demand Note
Loss Contingencies
Fifth Third Securities, Inc. (FTS) acted as the remarketing agent to issuers of VRDNs	$ 514			$ 514				$ 508
Letters of credit	5			5				94
Total Variable Rate Demand Notes	519			519				602
Letters of credit issued by the Bancorp related to variable rate demand notes	273			273				331
Variable Rate Demand Note | Trading Securities
Loss Contingencies
Total Variable Rate Demand Notes	15			15				1
Other Liabilities
Loss Contingencies
Reserve for unfunded commitments	129			129				161
Visa
Loss Contingencies
Recorded share of litigation formally settled by Visa and for probable future litigation settlements	$ 144			$ 144				$ 137
Visa IPO, shares of Visa's Class B common stock received																		10.1
Visa Class B shares carryover basis																		$ 0
Escrow Deposit							$ 600					$ 450	$ 150	$ 1,565	$ 400	$ 800	$ 500	$ 3,000

[1] Includes $ 41 and $ 62 of other short-term investments , $ 793 and $ 1,297 of portfolio loans and leases, $ (4) and $ (6) of ALLL, $ 5 and $ 7 of other assets, $ 1 and $ 2 of other liabilities, and $ 710 and $ 1,190 of long-term debt from consolidated VIEs that are included in their respe ctive captions above at September 30, 2018 and December 31, 2017 , respectively. For further information refer to Note 10 .