Fair Value - Level 3 Valuation - Nonrecurring (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, net of allowance for loan losses	$ 5,202	$ 3,744
Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	338	258
Mortgage loans held for investment, net of allowance for loan losses	134,684	127,763
Total nonrecurring assets at fair value	135,600	128,690
Nonrecurring | Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Quantitative Information [Line Items]
Total nonrecurring assets at fair value	3,105	2,497
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	455	113
Nonrecurring | Significant Unobservable Inputs (Level 3) | Single-Family
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	456	368
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	272	267
Nonrecurring | Significant Unobservable Inputs (Level 3) | Single-Family | Accepted Offer and Appraisal
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	172	74
Nonrecurring | Significant Unobservable Inputs (Level 3) | Single-Family | Internal Model and Walk Forward
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	284	294
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	1,825	1,471
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	176	172
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	259	448
Nonrecurring | Significant Unobservable Inputs (Level 3) | Multifamily | Asset Manager Estimate
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, net of allowance for loan losses	71	0
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	1,319	851
Nonrecurring | Significant Unobservable Inputs (Level 3) | Multifamily | Broker Price Opinion and Appraisal
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	$ 97	$ 278