Loans and Allowance for Credit Losses, PCI Loans Outstanding (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
PCI Loans UPB [Member]
PCI loans [Abstract]
Total PCI loans (unpaid principal balance)	$ 1,952	$ 7,348
PCI [Member]
PCI loans [Abstract]
PCI loans	1,174	5,009
PCI [Member] \| Total Commercial [Member]
PCI loans [Abstract]
PCI loans	0	4
PCI [Member] \| Total Consumer [Member]
PCI loans [Abstract]
PCI loans	1,174	5,005
PCI [Member] \| Real estate 1-4 family first mortgage [Member]
PCI loans [Abstract]
PCI loans	1,159	4,988
PCI [Member] \| Real estate 1-4 family junior lien mortgage [Member]
PCI loans [Abstract]
PCI loans	$ 15	$ 17

The undiscounted sum of all amounts, including amounts deemed principal, interest, fees, penalties, and other under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 15
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82894507&loc=d3e13503-111538

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

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