Loans and Allowance for Loan Losses - Loans in Consumer Portfolio an Purchased credit-impaired loans (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Loans disclosures
Nonaccrual	$ 680	$ 711
Consumer
Loans disclosures
Nonaccrual	150	184
Other consumer \| Consumer Loans Portfolio Segment [Member]
Loans disclosures
Nonaccrual	0	1
Residential mortgage and home equity \| Consumer Loans Portfolio Segment [Member]
Loans disclosures
Nonaccrual	$ 150	$ 183

Amount of financing receivable on nonaccrual status.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5111-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919258-210447

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