Fair Value Measurements - Measured on a Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
ASSETS
Mortgage loans held for sale	$ 5,720	$ 4,077
Forward MSRs - fair value	2,703	3,496
Fair Value, Recurring
ASSETS
Mortgage loans held for sale	5,720	4,077
Forward MSRs - fair value	2,703	3,496
LIABILITIES
Mortgage servicing rights financing	33	37
Excess spread financing	934	1,311
Fair Value, Recurring | Level 1
ASSETS
Mortgage loans held for sale	0	0
Forward MSRs - fair value	0	0
LIABILITIES
Mortgage servicing rights financing	0	0
Excess spread financing	0	0
Fair Value, Recurring | Level 2
ASSETS
Mortgage loans held for sale	5,720	4,077
Forward MSRs - fair value	0	0
LIABILITIES
Mortgage servicing rights financing	0	0
Excess spread financing	0	0
Fair Value, Recurring | Level 3
ASSETS
Mortgage loans held for sale	0	0
Forward MSRs - fair value	2,703	3,496
LIABILITIES
Mortgage servicing rights financing	33	37
Excess spread financing	934	1,311
IRLCs | Fair Value, Recurring
ASSETS
Derivative financial instruments	414	135
IRLCs | Fair Value, Recurring | Level 1
ASSETS
Derivative financial instruments	0	0
IRLCs | Fair Value, Recurring | Level 2
ASSETS
Derivative financial instruments	0	135
IRLCs | Fair Value, Recurring | Level 3
ASSETS
Derivative financial instruments	414	0
Forward MBS trades | Fair Value, Recurring
ASSETS
Derivative financial instruments	37	7
LIABILITIES
Derivative financial instruments	156	12
Forward MBS trades | Fair Value, Recurring | Level 1
ASSETS
Derivative financial instruments	0	0
LIABILITIES
Derivative financial instruments	0	0
Forward MBS trades | Fair Value, Recurring | Level 2
ASSETS
Derivative financial instruments	37	7
LIABILITIES
Derivative financial instruments	156	12
Forward MBS trades | Fair Value, Recurring | Level 3
ASSETS
Derivative financial instruments	0	0
LIABILITIES
Derivative financial instruments	0	0
LPCs | Fair Value, Recurring
ASSETS
Derivative financial instruments	38	12
LIABILITIES
Derivative financial instruments	1	3
LPCs | Fair Value, Recurring | Level 1
ASSETS
Derivative financial instruments	0	0
LIABILITIES
Derivative financial instruments	0	0
LPCs | Fair Value, Recurring | Level 2
ASSETS
Derivative financial instruments	0	12
LIABILITIES
Derivative financial instruments	0	3
LPCs | Fair Value, Recurring | Level 3
ASSETS
Derivative financial instruments	38	0
LIABILITIES
Derivative financial instruments	$ 1	$ 0