Loans and Allowance for Loan Losses - Loan Transfers from Held to Investment to Held for Sale and Proceeds from Sales of Loans (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Loans disclosures
Net Transfer of Loans Held for Investment to (from) Loans Held for Sale	$ 71	$ (91)
Proceeds from Sale	121	240
Commercial
Loans disclosures
Net Transfer of Loans Held for Investment to (from) Loans Held for Sale	71	(91)
Proceeds from Sale	121	240
Consumer
Loans disclosures
Net Transfer of Loans Held for Investment to (from) Loans Held for Sale	0	0
Proceeds from Sale	$ 0	$ 0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

+ Details

Name:	us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of financing receivables reclassified to held for sale during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

+ Details

Name:	us-gaap_FinancingReceivableReclassificationToHeldForSale
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of any significant sales of financing receivables during the reporting period.

+ References

+ Details

Name:	us-gaap_FinancingReceivableSignificantSales
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: