Fair Value Option Elected, Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Loans Receivable, Fair Value Disclosure	$ 177	$ 196
Trading Loans [Member]
Loans Receivable, Fair Value Disclosure	1,949	2,149
Aggregate Unpaid Principal Balance Under the Fair Value Option	(1,931)	(2,111)
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables	18	38
Loans Held-For-Sale [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans Receivable, Fair Value Disclosure		1
Aggregate Unpaid Principal Balance Under the Fair Value Option		(1)
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables		0
Loans Held-For-Sale [Member] \| Performing Financial Instruments [Member]
Loans Receivable, Fair Value Disclosure	2,005	1,576
Aggregate Unpaid Principal Balance Under the Fair Value Option	(1,945)	(1,533)
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables	60	43
Loans Held-For-Investment [Member] \| Performing Financial Instruments [Member]
Loans Receivable, Fair Value Disclosure	172	192
Aggregate Unpaid Principal Balance Under the Fair Value Option	(180)	(198)
Fair Value, Option, Loans Held as Assets, Aggregate Difference	(8)	(6)
Loans Held-For-Investment [Member] \| Nonperforming Financing Receivable [Member]
Loans Receivable, Fair Value Disclosure	5	4
Aggregate Unpaid Principal Balance Under the Fair Value Option	(8)	(6)
Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status, Aggregated Difference	(3)	(2)
Brokered Time Deposits [Member]
Obligations, Fair Value Disclosure	350	236
Aggregate Unpaid Principal Balance Under the Fair Value Option	(351)	(233)
Fair Value, Option, Aggregate Differences, Long-term Debt Instruments	(1)	3
Long-term Debt [Member]
Obligations, Fair Value Disclosure	220	530
Aggregate Unpaid Principal Balance Under the Fair Value Option	(214)	(517)
Fair Value, Option, Aggregate Differences, Long-term Debt Instruments	$ 6	$ 13

Aggregate Unpaid Principal Balance Under the Fair Value Option, Asset

No definition available.

Name:	sti_AggregateUnpaidPrincipalBalanceUndertheFairValueOptionAsset
Namespace Prefix:	sti_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of obligations measured on a recurring basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisObligations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of loans and long-term receivables (other than securities categorized as trading, available-for-sale or held-to-maturity) that have contractual principal amounts and for which the fair value option has been elected.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

+ Details

Name:	us-gaap_FairValueOptionAggregateDifferencesLoansAndLongTermReceivables
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of long-term debt instruments that have contractual principal amounts and for which the fair value option has been elected.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

+ Details

Name:	us-gaap_FairValueOptionAggregateDifferencesLongTermDebtInstruments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For loans held as assets for which the fair value option has been elected, this item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of those loans that are in nonaccrual status.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(3)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

+ Details

Name:	us-gaap_FairValueOptionLoansHeldAsAssetsAggregateAmountInNonaccrualStatusAggregatedDifference
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(3)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

+ Details

Name:	us-gaap_FairValueOptionLoansHeldAsAssetsAggregateDifference
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

+ Details

Name:	us-gaap_LoansReceivableFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancialInstrumentAxis=sti_TradingLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=sti_LoansHeldForSaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentPerformanceStatusAxis=us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentPerformanceStatusAxis=us-gaap_PerformingFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=sti_LoansHeldForInvestmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentPerformanceStatusAxis=us-gaap_NonperformingFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=sti_BrokeredTimeDepositsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_LongTermDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: