Commitments (Commitments, Contingent Liabilities and Guarantees - Additional Information) (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended			9 Months Ended			12 Months Ended
	Sep. 30, 2017		Sep. 30, 2016	Sep. 30, 2017		Sep. 30, 2016	Dec. 31, 2016		Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	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	$ 2,401			$ 2,401			$ 2,583
Margin account balance held by the brokerage clearing agent	15			15			15
Amount in excess of amounts reserved	31			31
Credit loss reserve	1,205	[1],[2]	$ 1,272	1,205	[1],[2]	$ 1,272	1,253	[1],[3]	$ 1,226	$ 1,226	$ 1,299	$ 1,299	$ 1,272
Residential Mortgage
Loss Contingencies
Amount in excess of amounts reserved	11			11
Outstanding balances on residential mortgage loans sold with representation and warranty provisions	10		18	10		18	13		$ 11		$ 21		$ 25
Outstanding balances on residential mortgage loans sold with credit recourse	$ 327			$ 327			$ 374
Delinquency Rates	3.00%			3.00%			3.20%
Credit loss reserve	$ 5			$ 5			$ 7
Repurchased Outstanding Principal	4		4	9		10
Repurchase Demand Request	4		$ 8	12		$ 18
Outstanding Repurchase Demand Inventory				1			2
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	$ 6			$ 6			$ 3
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	62.00%			62.00%			62.00%
Variable Rate Demand Note
Loss Contingencies
Fifth Third Securities, Inc. (FTS) acted as the remarketing agent to issuers of VRDNs	$ 615			$ 615			$ 784
Letters of credit	103			103			145
Total Variable Rate Demand Notes	718			718			929
Letters of credit issued by the Bancorp related to variable rate demand notes	436			436			609
Variable Rate Demand Note | Trading Securities
Loss Contingencies
Total Variable Rate Demand Notes	9			9			6
Other Liabilities
Loss Contingencies
Reserve for unfunded commitments	157			157			161
Other Liabilities | Residential Mortgage
Loss Contingencies
Outstanding balances on residential mortgage loans sold with representation and warranty provisions	10			10			13
Visa
Loss Contingencies
Recorded share of litigation formally settled by Visa and for probable future litigation settlements	$ 136			$ 136			$ 91
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 $ 116 and $ 85 of cash and due from banks, $ 1,532 and $ 1,216 of portfolio loans and leases , $ (8) and $ (26) of ALLL, $ 9 and $ 9 of other assets, $ 3 and $ 3 of other liabilities , and $ 1,491 and $ 1,094 of long-term debt from consolidated VIEs that are included in their respective captions above at September 30, 2017 and December 31, 2016 , respectively. For further information refer to Note 11 .

[2] Includes $ 1 related to leveraged leases at September 30, 2017 .

[3] Includes $ 2 related to leveraged leases at December 31, 2016 .