Commitments (Commitments, Contingent Liabilities and Guarantees - Additional Information) (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended			12 Months Ended
	Mar. 31, 2018		Mar. 31, 2017	Dec. 31, 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	$ 2,164			$ 2,185
Margin account balance held by the brokerage clearing agent	16			15
Amount in excess of amounts reserved	22
Credit loss reserve	1,138	[1],[2]	$ 1,238	1,196	[2],[3]	$ 1,253	[2],[3]
Residential Mortgage
Loss Contingencies
Amount in excess of amounts reserved	9
Outstanding balances on residential mortgage loans sold with representation and warranty provisions	8		12	9		$ 13
Outstanding balances on residential mortgage loans sold with credit recourse	$ 301			$ 312
Delinquency Rates	2.70%			3.00%
Credit loss reserve	$ 5			$ 5
Repurchased Outstanding Principal	2		2
Repurchase Demand Request	5		$ 3
Outstanding Repurchase Demand Inventory	2			1
Secured Debt
Loss Contingencies
Fully and unconditionally guaranteed certain long-term borrowing obligations issued by wholly-owned issuing trust entities	62			62
Standby Letters of Credit
Loss Contingencies
Reserve for unfunded commitments	$ 15			$ 6
Standby letters of credit as a percentage of total letters of credit	99.00%			99.00%
Standby Letters of Credit | Secured Debt
Loss Contingencies
Standby letters of credit as a percentage of total letters of credit	62.00%			61.00%
Variable Rate Demand Note
Loss Contingencies
Fifth Third Securities, Inc. (FTS) acted as the remarketing agent to issuers of VRDNs	$ 562			$ 508
Letters of credit	84			94
Total Variable Rate Demand Notes	646			602
Letters of credit issued by the Bancorp related to variable rate demand notes	320			331
Variable Rate Demand Note | Trading Securities
Loss Contingencies
Total Variable Rate Demand Notes	0			1
Other Liabilities
Loss Contingencies
Reserve for unfunded commitments	151			161
Other Liabilities | Residential Mortgage
Loss Contingencies
Outstanding balances on residential mortgage loans sold with representation and warranty provisions	8			9
Visa
Loss Contingencies
Recorded share of litigation formally settled by Visa and for probable future litigation settlements	$ 165			$ 137
Visa IPO, shares of Visa's Class B common stock received														10.1
Visa Class B shares carryover basis														$ 0
Escrow Deposit								$ 450	$ 150	$ 1,565	$ 400	$ 800	$ 500	$ 3,000

[1] Includes $ 1 related to leveraged leases at March 31, 2018 .

[2] Includes $ 66 and $ 62 of other short-term investments , $ 1,135 and $ 1,297 of portfolio loans and leases, $ (6) and $ (6) of ALLL, $ 6 and $ 7 of other assets, $ 2 and $ 2 of other liabilities, and $ 1,031 and $ 1,190 of long-term debt from consolidated VIEs that are included in their respe ctive captions above at March 31, 2018 and December 31, 2017 , respectively. For further information refer to Note 9 .

[3] Includes $ 1 related to leveraged leases at December 31, 2017 .