Fair Value Measurements - Measured on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Assets
Mortgage loans held for sale	$ 6,351	$ 5,720
Forward mortgage servicing rights	3,354	2,703
Liabilities
Mortgage servicing rights financing	23	33
Recurring Fair Value Measurements
Assets
Mortgage loans held for sale	6,351	5,720
Forward mortgage servicing rights	3,354	2,703
Liabilities
Mortgage servicing rights financing	23	33
Excess spread financing	934	934
Recurring Fair Value Measurements | IRLCs
Assets
Derivative asset, fair value	232	414
Liabilities
Derivative financial instruments	1
Recurring Fair Value Measurements | Forward MBS trades
Assets
Derivative asset, fair value	286	37
Liabilities
Derivative financial instruments	76	156
Recurring Fair Value Measurements | LPCs
Assets
Derivative asset, fair value	8	38
Liabilities
Derivative financial instruments	38	1
Recurring Fair Value Measurements | Swap futures
Liabilities
Derivative financial instruments	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
Liabilities
Derivative financial instruments	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 1 | Swap futures
Liabilities
Derivative financial instruments	0
Recurring Fair Value Measurements | Level 2
Assets
Mortgage loans held for sale	6,351	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
Liabilities
Derivative financial instruments	0
Recurring Fair Value Measurements | Level 2 | Forward MBS trades
Assets
Derivative asset, fair value	286	37
Liabilities
Derivative financial instruments	76	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 2 | Swap futures
Liabilities
Derivative financial instruments	1
Recurring Fair Value Measurements | Level 3
Assets
Mortgage loans held for sale	0	0
Forward mortgage servicing rights	3,354	2,703
Liabilities
Mortgage servicing rights financing	23	33
Excess spread financing	934	934
Recurring Fair Value Measurements | Level 3 | IRLCs
Assets
Derivative asset, fair value	232	414
Liabilities
Derivative financial instruments	1
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	8	38
Liabilities
Derivative financial instruments	38	$ 1
Recurring Fair Value Measurements | Level 3 | Swap futures
Liabilities
Derivative financial instruments	$ 0