Commitments - Commitment Risk Ratings (Details) - Commitments to Extend Credit - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Commitments	$ 79,076	$ 70,415
Pass
Line of Credit Facility [Line Items]
Commitments	78,124	69,928
Special Mention
Line of Credit Facility [Line Items]
Commitments	474	271
Substandard
Line of Credit Facility [Line Items]
Commitments	477	216
Doubtful
Line of Credit Facility [Line Items]
Commitments	$ 1	$ 0

Fair value portion of arrangements with third parties, including, but not limited to, operating lease arrangement and arrangement in which the entity has agreed to expend funds to procure goods or services, or has agreed to commit resources to supply goods or services.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(25))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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