Guarantees Mortgage Loans Repurchase Reserve Rollforward (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Guarantees [Abstract]
Reserve For Mortgage Loan Repurchase Losses	$ 39	$ 40

Liability for loss contingency of mortgage loans repurchased.

No definition available.

Name:	sti_ReserveForMortgageLoanRepurchaseLosses
Namespace Prefix:	sti_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant