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Fair Value Level 3 Valuation Inputs (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2016
Dec. 31, 2015
Fair Value Inputs, Quantitative Information [Line Items]    
Mortgage loans held for investment, at fair value $ 13,714 $ 14,075
Derivatives 673 866
Fannie Mae [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value (10,901) (11,133)
Consolidated Trusts [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value (28,563) (23,609)
Recurring Fair Value Measurements [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities 40,000 39,908
Available-for-sale securities 16,983 20,230
Mortgage loans held for investment, at fair value 13,714 14,075
Long-term Debt, Fair Value (39,464) (34,742)
Recurring Fair Value Measurements [Member] | Alt-A private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities 307 436
Available-for-sale securities 1,920 2,678
Recurring Fair Value Measurements [Member] | Subprime private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities 406 644
Available-for-sale securities 2,544 3,281
Recurring Fair Value Measurements [Member] | Mortgage revenue bonds [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities 363 449
Available-for-sale securities 2,564 2,701
Recurring Fair Value Measurements [Member] | Other [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Available-for-sale securities 940 1,404
Recurring Fair Value Measurements [Member] | Fannie Mae [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value (10,901) (11,133)
Recurring Fair Value Measurements [Member] | Fannie Mae [Member] | Senior Floating [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value (10,901) (11,133)
Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value (28,563) (23,609)
Significant Unobservable Inputs (Level 3) [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities 677 1,398
Available-for-sale securities 3,621 8,431
Mortgage loans held for investment, at fair value 411,028 351,355
Significant Unobservable Inputs (Level 3) [Member] | Fannie Mae [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Mortgage loans held for investment, at fair value 190,363 193,670
Long-term Debt, Fair Value (903) (898)
Significant Unobservable Inputs (Level 3) [Member] | Consolidated Trusts [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Mortgage loans held for investment, at fair value 220,665 157,685
Long-term Debt, Fair Value (31,112) (27,175)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities 677 1,398
Available-for-sale securities 3,621 8,431
Mortgage loans held for investment, at fair value 1,311 1,477
Derivatives 231 157
Long-term Debt, Fair Value (641) (865)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Agency [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities 26  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Alt-A private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities 245 305
Available-for-sale securities 177 1,041
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Subprime private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities 43 644
Available-for-sale securities 222 3,281
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Mortgage revenue bonds [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities 363 449
Available-for-sale securities 2,564 2,701
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Other [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Available-for-sale securities 655 1,404
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Alt-A private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities   305
Available-for-sale securities $ 106 $ 671
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Alt-A private-label securities [Member] | Trading Securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%)   1.30%
Prepayment Speed (%)   2.20%
Severity (%)   20.50%
Spreads (%)   2.19%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Alt-A private-label securities [Member] | Trading Securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%)   4.90%
Prepayment Speed (%)   4.50%
Severity (%)   95.00%
Spreads (%)   2.633%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Alt-A private-label securities [Member] | Trading Securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%)   3.60%
Prepayment Speed (%)   3.70%
Severity (%)   69.30%
Spreads (%)   2.531%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Alt-A private-label securities [Member] | Available-for-sale securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 4.00% 0.50%
Prepayment Speed (%) 5.00% 1.70%
Severity (%) 50.00% 1.40%
Spreads (%) 3.064% 2.256%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Alt-A private-label securities [Member] | Available-for-sale securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 6.00% 40.70%
Prepayment Speed (%) 7.00% 72.60%
Severity (%) 70.00% 95.00%
Spreads (%) 3.823% 2.804%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Alt-A private-label securities [Member] | Available-for-sale securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 4.20% 3.40%
Prepayment Speed (%) 5.20% 13.50%
Severity (%) 55.50% 58.50%
Spreads (%) 3.727% 2.60%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Subprime private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities   $ 526
Available-for-sale securities $ 170 $ 1,848
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Subprime private-label securities [Member] | Trading Securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%)   4.20%
Prepayment Speed (%)   0.40%
Severity (%)   55.90%
Spreads (%)   2.85%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Subprime private-label securities [Member] | Trading Securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%)   8.40%
Prepayment Speed (%)   5.30%
Severity (%)   95.00%
Spreads (%)   2.85%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Subprime private-label securities [Member] | Trading Securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%)   5.90%
Prepayment Speed (%)   3.30%
Severity (%)   73.70%
Spreads (%)   2.85%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Subprime private-label securities [Member] | Available-for-sale securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 5.00% 0.50%
Prepayment Speed (%) 3.00% 0.50%
Severity (%) 88.00% 20.00%
Spreads (%) 4.319% 2.55%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Subprime private-label securities [Member] | Available-for-sale securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 7.00% 11.30%
Prepayment Speed (%) 4.00% 11.20%
Severity (%) 95.00% 95.00%
Spreads (%) 4.803% 2.85%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Subprime private-label securities [Member] | Available-for-sale securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 6.00% 5.90%
Prepayment Speed (%) 3.50% 3.80%
Severity (%) 91.50% 79.00%
Spreads (%) 4.558% 2.833%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Other [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Available-for-sale securities $ 97 $ 683
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Other [Member] | Available-for-sale securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 3.50% 0.50%
Prepayment Speed (%) 2.50% 2.50%
Severity (%) 88.00% 6.60%
Spreads (%) 3.581% 2.00%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Other [Member] | Available-for-sale securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 3.50% 4.60%
Prepayment Speed (%) 3.00% 15.50%
Severity (%) 88.00% 95.00%
Spreads (%) 4.791% 4.544%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Other [Member] | Available-for-sale securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 3.50% 3.40%
Prepayment Speed (%) 2.80% 4.70%
Severity (%) 88.00% 65.70%
Spreads (%) 4.135% 3.156%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus without Inputs [Member] | Agency [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities $ 25  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus without Inputs [Member] | Alt-A private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities 60  
Available-for-sale securities   $ 201
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus without Inputs [Member] | Subprime private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities   73
Available-for-sale securities   945
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Alt-A private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities 185  
Available-for-sale securities $ 71 $ 169
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Alt-A private-label securities [Member] | Trading Securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 0.90%  
Prepayment Speed (%) 2.00%  
Severity (%) 95.00%  
Spreads (%) 3.392%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Alt-A private-label securities [Member] | Trading Securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 4.00%  
Prepayment Speed (%) 6.00%  
Severity (%) 95.00%  
Spreads (%) 6.448%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Alt-A private-label securities [Member] | Trading Securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 3.40%  
Prepayment Speed (%) 5.30%  
Severity (%) 95.00%  
Spreads (%) 5.877%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Alt-A private-label securities [Member] | Available-for-sale securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 3.50% 4.00%
Prepayment Speed (%) 4.00% 4.00%
Severity (%) 41.00% 50.00%
Spreads (%) 3.113% 2.60%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Alt-A private-label securities [Member] | Available-for-sale securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 6.00% 5.00%
Prepayment Speed (%) 7.50% 7.50%
Severity (%) 56.00% 64.00%
Spreads (%) 4.06% 3.694%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Alt-A private-label securities [Member] | Available-for-sale securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 4.50% 4.80%
Prepayment Speed (%) 5.40% 6.40%
Severity (%) 50.10% 59.20%
Spreads (%) 3.847% 2.965%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Subprime private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities $ 43  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Subprime private-label securities [Member] | Trading Securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 4.40%  
Prepayment Speed (%) 4.80%  
Severity (%) 56.00%  
Spreads (%) 7.249%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Subprime private-label securities [Member] | Trading Securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 4.40%  
Prepayment Speed (%) 4.80%  
Severity (%) 56.00%  
Spreads (%) 7.249%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Subprime private-label securities [Member] | Trading Securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 4.40%  
Prepayment Speed (%) 4.80%  
Severity (%) 56.00%  
Spreads (%) 7.249%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Mortgage revenue bonds [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities $ 353 $ 437
Available-for-sale securities $ 1,420 $ 1,462
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Mortgage revenue bonds [Member] | Trading Securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Spreads (%) 0.235% 0.015%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Mortgage revenue bonds [Member] | Trading Securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Spreads (%) 3.486% 3.762%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Mortgage revenue bonds [Member] | Trading Securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Spreads (%) 3.19% 2.989%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Mortgage revenue bonds [Member] | Available-for-sale securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Spreads (%) 0.035% (0.158%)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Mortgage revenue bonds [Member] | Available-for-sale securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Spreads (%) 4.246% 3.791%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Mortgage revenue bonds [Member] | Available-for-sale securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Spreads (%) 3.13% 2.838%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Other [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Available-for-sale securities $ 546 $ 520
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Other [Member] | Available-for-sale securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 2.10% 0.00%
Prepayment Speed (%) 0.80% 0.00%
Severity (%) 4.00% 95.00%
Spreads (%) 2.35% 2.60%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Other [Member] | Available-for-sale securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 3.80% 1.80%
Prepayment Speed (%) 6.00% 0.50%
Severity (%) 95.00% 95.00%
Spreads (%) 4.87% 3.50%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Other [Member] | Available-for-sale securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 3.70% 0.00%
Prepayment Speed (%) 5.90% 0.00%
Severity (%) 6.30% 95.00%
Spreads (%) 4.755% 3.236%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor with Inputs [Member] | Subprime private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Available-for-sale securities   $ 343
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor with Inputs [Member] | Subprime private-label securities [Member] | Available-for-sale securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%)   2.50%
Prepayment Speed (%)   1.90%
Severity (%)   67.60%
Spreads (%)   2.85%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor with Inputs [Member] | Subprime private-label securities [Member] | Available-for-sale securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%)   7.50%
Prepayment Speed (%)   5.70%
Severity (%)   85.70%
Spreads (%)   3.40%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor with Inputs [Member] | Subprime private-label securities [Member] | Available-for-sale securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%)   4.80%
Prepayment Speed (%)   3.30%
Severity (%)   72.70%
Spreads (%)   2.996%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor with Inputs [Member] | Mortgage revenue bonds [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Available-for-sale securities $ 988 $ 991
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor with Inputs [Member] | Mortgage revenue bonds [Member] | Available-for-sale securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Spreads (%) 0.035% (0.331%)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor with Inputs [Member] | Mortgage revenue bonds [Member] | Available-for-sale securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Spreads (%) 3.956% 3.868%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor with Inputs [Member] | Mortgage revenue bonds [Member] | Available-for-sale securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Spreads (%) 0.578% 0.379%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Other Valuation Technique without Inputs [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Derivatives $ 44 $ 4
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Other Valuation Technique without Inputs [Member] | Agency [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities 1  
Available-for-sale securities 3 4
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Other Valuation Technique without Inputs [Member] | Subprime private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities   45
Available-for-sale securities 52 145
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Other Valuation Technique without Inputs [Member] | Mortgage revenue bonds [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading Securities 10 12
Available-for-sale securities 156 248
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Other Valuation Technique without Inputs [Member] | Other [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Available-for-sale securities 12 201
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Dealer Mark without Inputs [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Derivatives 187 136
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Internal Model [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Derivatives   17
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-family [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Mortgage loans held for investment, at fair value 1,160 1,321
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-family [Member] | Consensus with Inputs [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Mortgage loans held for investment, at fair value $ 105 $ 234
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-family [Member] | Consensus with Inputs [Member] | Mortgage Loans [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 0.50% 0.50%
Prepayment Speed (%) 1.00% 2.50%
Severity (%) 20.00% 20.00%
Spreads (%) 2.687% 2.55%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-family [Member] | Consensus with Inputs [Member] | Mortgage Loans [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 4.90% 5.00%
Prepayment Speed (%) 13.80% 26.00%
Severity (%) 95.00% 89.10%
Spreads (%) 3.45% 2.776%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-family [Member] | Consensus with Inputs [Member] | Mortgage Loans [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 2.30% 3.70%
Prepayment Speed (%) 5.80% 6.40%
Severity (%) 74.40% 69.00%
Spreads (%) 2.781% 2.646%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-family [Member] | Consensus without Inputs [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Mortgage loans held for investment, at fair value $ 261 $ 274
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-family [Member] | Build-Up with inputs [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Mortgage loans held for investment, at fair value $ 120 $ 127
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-family [Member] | Build-Up with inputs [Member] | Mortgage Loans [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 0.00% 0.00%
Prepayment Speed (%) 3.60% 3.00%
Severity (%) 0.00% 0.00%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-family [Member] | Build-Up with inputs [Member] | Mortgage Loans [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 98.70% 99.20%
Prepayment Speed (%) 100.00% 100.00%
Severity (%) 100.00% 100.00%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-family [Member] | Build-Up with inputs [Member] | Mortgage Loans [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 36.70% 34.80%
Prepayment Speed (%) 10.80% 10.40%
Severity (%) 40.00% 39.90%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-family [Member] | Build-Up without Inputs [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Mortgage loans held for investment, at fair value $ 602 $ 632
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-family [Member] | Other Valuation Technique without Inputs [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Mortgage loans held for investment, at fair value 72 54
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Multifamily [Member] | Build-Up with inputs [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Mortgage loans held for investment, at fair value $ 151 $ 156
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Multifamily [Member] | Build-Up with inputs [Member] | Mortgage Loans [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Spreads (%) 0.70% 0.70%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Multifamily [Member] | Build-Up with inputs [Member] | Mortgage Loans [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Spreads (%) 3.642% 3.272%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Multifamily [Member] | Build-Up with inputs [Member] | Mortgage Loans [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Spreads (%) 1.799% 1.588%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Fannie Mae [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value $ (395) $ (369)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Fannie Mae [Member] | Senior Floating [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value (395) (369)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Fannie Mae [Member] | Discounted Cash Flow without Inputs [Member] | Senior Floating [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value (395) (369)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value (246) (496)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Consensus with Inputs [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value   $ (181)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Consensus with Inputs [Member] | Long-term debt [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%)   0.50%
Prepayment Speed (%)   2.50%
Severity (%)   20.00%
Spreads (%)   2.55%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Consensus with Inputs [Member] | Long-term debt [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%)   3.80%
Prepayment Speed (%)   26.00%
Severity (%)   80.60%
Spreads (%)   2.70%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Consensus with Inputs [Member] | Long-term debt [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%)   3.40%
Prepayment Speed (%)   5.60%
Severity (%)   67.80%
Spreads (%)   2.658%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Consensus without Inputs [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value (118) $ (149)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Other Valuation Technique without Inputs [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value $ (128) $ (166)