Fair Value - Valuation Inputs (Details)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale	$ 837,000,000	$ 1,697,000,000
Net derivatives	171,000,000	1,046,000,000
Mortgage loans	4,964,000,000	6,490,000,000
Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	88,206,000,000	136,542,000,000
Available-for-sale	837,000,000	1,697,000,000
Mortgage loans	4,964,000,000	6,490,000,000
Total nonrecurring assets at fair value	94,428,000,000	147,074,000,000
Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	57,000,000	95,000,000
Available-for-sale	753,000,000	648,000,000
Mortgage loans held for sale, at lower of cost or fair value	5,307,000,000	5,502,000,000
Mortgage loans	209,090,000,000	255,556,000,000
Total nonrecurring assets at fair value	215,567,000,000	262,442,000,000
Significant Unobservable Inputs (Level 3) | Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	57,000,000	95,000,000
Available-for-sale	753,000,000	648,000,000
Net derivatives	131,000,000	333,000,000
Mortgage loans	755,000,000	861,000,000
Total nonrecurring assets at fair value	1,717,000,000	1,986,000,000
Significant Unobservable Inputs (Level 3) | Recurring | Discounted Cash Flow
Fair Value Inputs, Quantitative Information [Line Items]
Net derivatives	(21,000,000)	130,000,000
Significant Unobservable Inputs (Level 3) | Recurring | Dealer Mark
Fair Value Inputs, Quantitative Information [Line Items]
Net derivatives	152,000,000	203,000,000
Significant Unobservable Inputs (Level 3) | Nonrecurring
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	1,584,000,000	1,087,000,000
Total nonrecurring assets at fair value	2,872,000,000	2,742,000,000
Significant Unobservable Inputs (Level 3) | Nonrecurring | Single-Family
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	209,000,000	261,000,000
Significant Unobservable Inputs (Level 3) | Nonrecurring | Multifamily
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans	178,000,000	390,000,000
Significant Unobservable Inputs (Level 3) | Nonrecurring | Various | Single-Family
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	11,000,000	11,000,000
Significant Unobservable Inputs (Level 3) | Nonrecurring | Various | Multifamily
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	34,000,000	25,000,000
Significant Unobservable Inputs (Level 3) | Nonrecurring | Consensus
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	201,000,000	754,000,000
Significant Unobservable Inputs (Level 3) | Nonrecurring | Single Vendor
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	1,383,000,000	333,000,000
Significant Unobservable Inputs (Level 3) | Nonrecurring | Internal Model | Single-Family
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans	867,000,000	979,000,000
Acquired property, net	75,000,000	41,000,000
Significant Unobservable Inputs (Level 3) | Nonrecurring | Internal Model | Multifamily
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans	23,000,000	125,000,000
Significant Unobservable Inputs (Level 3) | Nonrecurring | Appraisal | Single-Family
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	73,000,000	89,000,000
Significant Unobservable Inputs (Level 3) | Nonrecurring | Appraisal | Multifamily
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans	37,000,000	225,000,000
Significant Unobservable Inputs (Level 3) | Nonrecurring | Broker Price Opinion | Multifamily
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans	118,000,000	40,000,000
Significant Unobservable Inputs (Level 3) | Nonrecurring | Accepted Offer | Single-Family
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	13,000,000	35,000,000
Significant Unobservable Inputs (Level 3) | Nonrecurring | Walk Forward | Single-Family
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	37,000,000	85,000,000
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	83,581,000,000	130,456,000,000
Available-for-sale	0	0
Mortgage loans held for sale, at lower of cost or fair value	0	0
Mortgage loans	0	0
Total nonrecurring assets at fair value	148,112,000,000	227,635,000,000
Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	83,581,000,000	130,456,000,000
Available-for-sale	0	0
Mortgage loans	0	0
Total nonrecurring assets at fair value	83,831,000,000	131,576,000,000
Quoted Prices in Active Markets for Identical Assets (Level 1) | Nonrecurring
Fair Value Inputs, Quantitative Information [Line Items]
Total nonrecurring assets at fair value	0	0
Significant Other Observable Inputs (Level 2)
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	4,568,000,000	5,991,000,000
Available-for-sale	84,000,000	1,049,000,000
Mortgage loans held for sale, at lower of cost or fair value	178,000,000	116,000,000
Mortgage loans	3,796,917,000,000	3,512,672,000,000
Total nonrecurring assets at fair value	3,875,259,000,000	3,578,668,000,000
Significant Other Observable Inputs (Level 2) | Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	4,568,000,000	5,991,000,000
Available-for-sale	84,000,000	1,049,000,000
Mortgage loans	4,209,000,000	5,629,000,000
Total nonrecurring assets at fair value	9,117,000,000	14,417,000,000
Significant Other Observable Inputs (Level 2) | Nonrecurring
Fair Value Inputs, Quantitative Information [Line Items]
Other liabilities, fair value	0	0
Mortgage loans held for sale, at lower of cost or fair value	38,000,000	25,000,000
Agency | Significant Unobservable Inputs (Level 3) | Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale	431,000,000	195,000,000
Agency | Significant Unobservable Inputs (Level 3) | Recurring | Various
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	57,000,000	95,000,000
Available-for-sale	52,000,000	98,000,000
Agency | Significant Unobservable Inputs (Level 3) | Recurring | Consensus
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale	379,000,000	97,000,000
Private-label and other mortgage securities | Significant Unobservable Inputs (Level 3) | Recurring | Various
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale		2,000,000
Mortgage revenue bonds | Significant Unobservable Inputs (Level 3) | Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale	144,000,000	216,000,000
Mortgage revenue bonds | Significant Unobservable Inputs (Level 3) | Recurring | Various
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale	50,000,000	72,000,000
Mortgage revenue bonds | Significant Unobservable Inputs (Level 3) | Recurring | Single Vendor
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale	94,000,000	144,000,000
Other | Significant Unobservable Inputs (Level 3) | Recurring
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale	176,000,000	235,000,000
Other | Significant Unobservable Inputs (Level 3) | Recurring | Various
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale	1,000,000	29,000,000
Other | Significant Unobservable Inputs (Level 3) | Recurring | Discounted Cash Flow
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale	$ 175,000,000	$ 206,000,000
Other | Significant Unobservable Inputs (Level 3) | Recurring | Discounted Cash Flow | Available-for-sale securities | Minimum | Default rate
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, measurement input	0.04090	0.04250
Other | Significant Unobservable Inputs (Level 3) | Recurring | Discounted Cash Flow | Available-for-sale securities | Maximum | Default rate
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, measurement input	0.04340	0.04430
Other | Significant Unobservable Inputs (Level 3) | Recurring | Discounted Cash Flow | Available-for-sale securities | Weighted average | Default rate
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, measurement input	0.04220	0.04342
Subprime | Significant Unobservable Inputs (Level 3) | Recurring | Various
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale	$ 2,000,000
Single Vendor | Significant Unobservable Inputs (Level 3) | Recurring | Single Vendor | Available-for-sale securities | Minimum | Default rate
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, measurement input	0.00093	0.00320
Single Vendor | Significant Unobservable Inputs (Level 3) | Recurring | Single Vendor | Available-for-sale securities | Maximum | Default rate
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, measurement input	0.00494	0.03153
Single Vendor | Significant Unobservable Inputs (Level 3) | Recurring | Single Vendor | Available-for-sale securities | Weighted average | Default rate
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale, measurement input	0.00272	0.00934