Mortgage Loans Held for Sale - Held For Sale (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans held for sale - UPB	$ 5,438	$ 3,949
Mark-to-market adjustment	282	128
Total mortgage loans held for sale	5,720	4,077	$ 1,631
UPB	64	29
Fair Value	54	22
Ginnie Mae Repurchased Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB	$ 44	$ 25

Amount, before valuation allowance, of financing receivable classified as held-for-sale.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=120238483&loc=d3e48678-111004

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