Business Combinations and Asset Acquisitions (Details)		3 Months Ended		9 Months Ended
	Jul. 31, 2023 USD ($)	Jun. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Jul. 24, 2024 USD ($)	Aug. 01, 2023 USD ($) $ / shares
Business Acquisition [Line Items]
Asset Acquisition, Consideration Transferred			$ 34,000,000
Adjustment/Recognition of bargain purchase gain				$ 4,000,000	$ 96,000,000
Business Combination, Description [Abstract]
Business Combination, Bargain Purchase, Gain, Statement of Income or Comprehensive Income [Extensible Enumeration]			Other expenses, net
Flagstar Bank, N.A.
Business Combination, Description [Abstract]
Asset Acquisition, Customers acquired, Amount						1,300,000
Flagstar Bank, N.A. | Mortgage servicing rights
Business Combination, Description [Abstract]
Asset Acquisition, Assets Acquired, Amount						$ 1,100,000,000
Asset Acquisition, Assets Acquired, UPB						$ 350,000,000,000
Home Point Capital Inc [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred			$ 658,000,000
Business Combination, Consideration Transferred for MSRs			335,000,000
Business Combination, Consideration Transferred for Tender Offer			$ 323,000,000
Price per share (in dollars per share) | $ / shares							$ 2.33
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Mortgage Servicing Rights							$ 1,200,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Senior Note							$ 500,000,000
Business Combination, Description [Abstract]
Business Combination, Bargain Purchase, Gain Recognized, Description			The Company believes it was able to negotiate a bargain purchase price due to seller’s operational challenges from significant market volatility, as well as the seller’s desire to exit the business in an expedited manner.
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other liabilities [Abstract]		$ 4,000,000
Home Point Capital Inc [Member] | Corporate and other
Business Acquisition [Line Items]
Adjustment/Recognition of bargain purchase gain		4,000,000	$ 96,000,000
Business Combination, Description [Abstract]
Business Combination, Bargain Purchase, Gain Recognized, Final Amount		$ 92,000,000
Roosevelt
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 28,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	$ 4,000,000
Goodwill acquired			21,000,000
Roosevelt | Servicing
Business Acquisition [Line Items]
Goodwill acquired			5,000,000
Roosevelt | Corporate and other
Business Acquisition [Line Items]
Goodwill acquired			$ 16,000,000