Fair Value - Level 3 Valuation - Nonrecurring (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, net of allowance for loan losses	$ 3,176,000,000	$ 3,315,000,000
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Inputs, Quantitative Information [Line Items]
Total nonrecurring assets at fair value	80,880,000,000	81,745,000,000
Mortgage loans held-for-sale, at lower of cost or fair value	0	0
Mortgage loans held for investment, net of allowance for loan losses	0	0
Significant Other Observable Inputs (Level 2)
Fair Value Inputs, Quantitative Information [Line Items]
Total nonrecurring assets at fair value	3,572,424,000,000	3,643,669,000,000
Mortgage loans held-for-sale, at lower of cost or fair value	277,000,000	93,000,000
Mortgage loans held for investment, net of allowance for loan losses	3,494,262,000,000	3,571,555,000,000
Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Quantitative Information [Line Items]
Total nonrecurring assets at fair value	132,907,000,000	133,003,000,000
Mortgage loans held-for-sale, at lower of cost or fair value	1,793,000,000	2,196,000,000
Mortgage loans held for investment, net of allowance for loan losses	130,364,000,000	130,022,000,000
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Inputs, Quantitative Information [Line Items]
Total nonrecurring assets at fair value	0	0
Nonrecurring | Significant Other Observable Inputs (Level 2)
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held-for-sale, at lower of cost or fair value	66,000,000	42,000,000
Total nonrecurring liabilities at fair value	0	0
Nonrecurring | Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Quantitative Information [Line Items]
Total nonrecurring assets at fair value	1,696,000,000	3,993,000,000
Total nonrecurring liabilities at fair value	0	0
Nonrecurring | Significant Unobservable Inputs (Level 3) | Consensus
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held-for-sale, at lower of cost or fair value	304,000,000	1,994,000,000
Nonrecurring | Significant Unobservable Inputs (Level 3) | Single-Family
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	307,000,000	390,000,000
Nonrecurring | Significant Unobservable Inputs (Level 3) | Single-Family | Internal Model
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, net of allowance for loan losses	281,000,000	407,000,000
Acquired property, net	145,000,000	230,000,000
Nonrecurring | Significant Unobservable Inputs (Level 3) | Single-Family | Appraisal
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	53,000,000	43,000,000
Nonrecurring | Significant Unobservable Inputs (Level 3) | Single-Family | Accepted Offer
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	28,000,000	23,000,000
Nonrecurring | Significant Unobservable Inputs (Level 3) | Single-Family | Walk Forward
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	65,000,000	75,000,000
Nonrecurring | Significant Unobservable Inputs (Level 3) | Single-Family | Various
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	16,000,000	19,000,000
Nonrecurring | Significant Unobservable Inputs (Level 3) | Multifamily
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, net of allowance for loan losses	801,000,000	1,020,000,000
Nonrecurring | Significant Unobservable Inputs (Level 3) | Multifamily | Internal Model
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, net of allowance for loan losses	193,000,000	218,000,000
Nonrecurring | Significant Unobservable Inputs (Level 3) | Multifamily | Appraisal
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, net of allowance for loan losses	168,000,000	33,000,000
Nonrecurring | Significant Unobservable Inputs (Level 3) | Multifamily | Broker Price Opinion
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, net of allowance for loan losses	440,000,000	769,000,000
Nonrecurring | Significant Unobservable Inputs (Level 3) | Multifamily | Various
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	$ 3,000,000	$ 182,000,000