Fair Value Measurements - Measured on a Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Assets
Mortgage loans held for sale	$ 6,961	$ 5,720
Liabilities
Mortgage servicing rights financing	21	33
Recurring Fair Value Measurements
Assets
Mortgage loans held for sale	6,961	5,720
Forward mortgage servicing rights	3,307	2,703
Liabilities
Mortgage servicing rights financing	21	33
Excess spread financing	867	934
Recurring Fair Value Measurements | IRLCs
Assets
Derivative asset, fair value	204	414
Recurring Fair Value Measurements | Forward MBS trades
Assets
Derivative asset, fair value	27	37
Liabilities
Derivative financial instruments	25	156
Recurring Fair Value Measurements | LPCs
Assets
Derivative asset, fair value	10	38
Liabilities
Derivative financial instruments	1	1
Recurring Fair Value Measurements | Level 1
Assets
Mortgage loans held for sale	0	0
Forward mortgage servicing rights	0	0
Liabilities
Mortgage servicing rights financing	0	0
Excess spread financing	0	0
Recurring Fair Value Measurements | Level 1 | IRLCs
Assets
Derivative asset, fair value	0	0
Recurring Fair Value Measurements | Level 1 | Forward MBS trades
Assets
Derivative asset, fair value	0	0
Liabilities
Derivative financial instruments	0	0
Recurring Fair Value Measurements | Level 1 | LPCs
Assets
Derivative asset, fair value	0	0
Liabilities
Derivative financial instruments	0	0
Recurring Fair Value Measurements | Level 2
Assets
Mortgage loans held for sale	6,961	5,720
Forward mortgage servicing rights	0	0
Liabilities
Mortgage servicing rights financing	0	0
Excess spread financing	0	0
Recurring Fair Value Measurements | Level 2 | IRLCs
Assets
Derivative asset, fair value	0	0
Recurring Fair Value Measurements | Level 2 | Forward MBS trades
Assets
Derivative asset, fair value	27	37
Liabilities
Derivative financial instruments	25	156
Recurring Fair Value Measurements | Level 2 | LPCs
Assets
Derivative asset, fair value	0	0
Liabilities
Derivative financial instruments	0	0
Recurring Fair Value Measurements | Level 3
Assets
Mortgage loans held for sale	0	0
Forward mortgage servicing rights	3,307	2,703
Liabilities
Mortgage servicing rights financing	21	33
Excess spread financing	867	934
Recurring Fair Value Measurements | Level 3 | IRLCs
Assets
Derivative asset, fair value	204	414
Recurring Fair Value Measurements | Level 3 | Forward MBS trades
Assets
Derivative asset, fair value	0	0
Liabilities
Derivative financial instruments	0	0
Recurring Fair Value Measurements | Level 3 | LPCs
Assets
Derivative asset, fair value	10	38
Liabilities
Derivative financial instruments	$ 1	$ 1