Commitments - Activity in Reserve for Representation and Warranty Provisions (Details) - Residential Mortgage - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance, beginning of period	$ 8	$ 8	$ 6	$ 9
Net (reductions) additions to the reserve	(1)	(1)	1	(2)
Balance, end of period	$ 7	$ 7	$ 7	$ 7

Amount of increase (decrease) in valuation and qualifying accounts and reserves.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09)
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

Name:	us-gaap_ValuationAllowancesAndReservesPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration