MSR - Additional Information (Details) - USD ($) $ in Billions	Sep. 30, 2019	Dec. 31, 2018
Disclosure - Activity Related to Mortgage Banking Net Revenue [Abstract]
Aggregate loans transferred to securitization	$ 82.7	$ 63.2

This is the principal amount outstanding for securitized loans only (across all types of loans).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118948506&loc=d3e107314-111719

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