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Fair Value Level 3 Valuation Inputs (Details) - USD ($)
$ in Millions
 6 Months Ended 12 Months Ended
Jun. 30, 2016
Dec. 31, 2015
Fair Value Inputs, Quantitative Information [Line Items]    
Mortgage loans held for investment, at fair value $ 13,413 $ 14,075
Derivatives 748 866
Fannie Mae [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value (10,650) (11,133)
Consolidated Trusts [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value (32,798) (23,609)
Recurring Fair Value Measurements [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading securities 39,167 39,908
Available-for-sale securities 13,180 20,230
Mortgage loans held for investment, at fair value 13,413 14,075
Long-term Debt, Fair Value (43,448) (34,742)
Recurring Fair Value Measurements [Member] | Alt-A private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading securities 316 436
Available-for-sale securities 1,827 2,678
Recurring Fair Value Measurements [Member] | Subprime private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading securities 395 644
Available-for-sale securities 2,373 3,281
Recurring Fair Value Measurements [Member] | Mortgage revenue bonds [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading securities 193 449
Available-for-sale securities 2,029 2,701
Recurring Fair Value Measurements [Member] | Other [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Available-for-sale securities 488 1,404
Recurring Fair Value Measurements [Member] | Fannie Mae [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value (10,650) (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 (10,650) (11,133)
Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value (32,798) (23,609)
Significant Unobservable Inputs (Level 3) [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading securities 496 1,398
Available-for-sale securities 2,828 8,431
Mortgage loans held for investment, at fair value 415,125 351,355
Significant Unobservable Inputs (Level 3) [Member] | Fannie Mae [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Mortgage loans held for investment, at fair value 183,942 193,670
Long-term Debt, Fair Value (881) (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 231,183 157,685
Long-term Debt, Fair Value (40,138) (27,175)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading securities 496 1,398
Available-for-sale securities 2,828 8,431
Mortgage loans held for investment, at fair value 1,280 1,477
Derivatives 248 157
Long-term Debt, Fair Value (736) (865)
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 259 305
Available-for-sale securities 175 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 44 644
Available-for-sale securities 173 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 193 449
Available-for-sale securities 2,029 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 450 1,404
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Alt-A private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Trading securities $ 37  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Alt-A private-label securities [Member] | Trading securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 1.80%  
Prepayment Speed (%) 3.10%  
Severity (%) 72.00%  
Spreads (%) 3.355%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Alt-A private-label securities [Member] | Trading securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 1.80%  
Prepayment Speed (%) 3.10%  
Severity (%) 72.00%  
Spreads (%) 3.355%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Alt-A private-label securities [Member] | Trading securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 1.80%  
Prepayment Speed (%) 3.10%  
Severity (%) 72.00%  
Spreads (%) 3.355%  
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]    
Trading securities $ 44  
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] | Trading securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 5.00%  
Prepayment Speed (%) 5.00%  
Severity (%) 75.00%  
Spreads (%) 6.678%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Subprime private-label securities [Member] | Trading securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 5.00%  
Prepayment Speed (%) 5.00%  
Severity (%) 75.00%  
Spreads (%) 6.678%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Subprime private-label securities [Member] | Trading securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 5.00%  
Prepayment Speed (%) 5.00%  
Severity (%) 75.00%  
Spreads (%) 6.678%  
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 $ 951 $ 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 (%) 0.075% (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 (%) 4.143% 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 (%) 0.603% 0.379%
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 $ 222 $ 305
Available-for-sale securities $ 121 $ 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 (%) 2.00% 1.30%
Prepayment Speed (%) 3.00% 2.20%
Severity (%) 50.00% 20.50%
Spreads (%) 2.80% 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 (%) 5.00% 4.90%
Prepayment Speed (%) 8.00% 4.50%
Severity (%) 95.00% 95.00%
Spreads (%) 4.934% 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 (%) 4.20% 3.60%
Prepayment Speed (%) 6.70% 3.70%
Severity (%) 83.30% 69.30%
Spreads (%) 4.378% 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 (%) 3.00% 0.50%
Prepayment Speed (%) 5.00% 1.70%
Severity (%) 60.00% 1.40%
Spreads (%) 3.025% 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 (%) 8.00% 72.60%
Severity (%) 80.00% 95.00%
Spreads (%) 3.42% 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 (%) 3.40% 3.40%
Prepayment Speed (%) 5.20% 13.50%
Severity (%) 61.60% 58.50%
Spreads (%) 3.302% 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   $ 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 (%)   0.50%
Prepayment Speed (%)   0.50%
Severity (%)   20.00%
Spreads (%)   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 (%)   11.30%
Prepayment Speed (%)   11.20%
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] | Available-for-sale securities [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%)   5.90%
Prepayment Speed (%)   3.80%
Severity (%)   79.00%
Spreads (%)   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 $ 87 $ 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 (%) 0.50% 0.50%
Prepayment Speed (%) 2.50% 2.50%
Severity (%) 20.00% 6.60%
Spreads (%) 3.035% 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 (%) 5.00% 15.50%
Severity (%) 88.00% 95.00%
Spreads (%) 4.53% 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 (%) 2.50% 4.70%
Severity (%) 87.70% 65.70%
Spreads (%) 3.761% 3.156%
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]    
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]    
Available-for-sale securities $ 54 $ 169
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 (%) 6.00% 4.00%
Prepayment Speed (%) 8.00% 4.00%
Severity (%) 65.00% 50.00%
Spreads (%) 3.016% 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 (%) 8.00% 7.50%
Severity (%) 65.00% 64.00%
Spreads (%) 3.67% 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 (%) 6.00% 4.80%
Prepayment Speed (%) 8.00% 6.40%
Severity (%) 65.00% 59.20%
Spreads (%) 3.552% 2.965%
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 $ 185 $ 437
Available-for-sale securities $ 970 $ 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 (%) 0.275% 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 (%) 3.214% 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 (%) 3.173% 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 (%) 0.075% (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 (%) 4.428% 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 (%) 2.868% 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 $ 357 $ 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 (%) 0.80% 0.00%
Prepayment Speed (%) 1.00% 0.00%
Severity (%) 95.00% 95.00%
Spreads (%) 2.20% 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 (%) 0.80% 1.80%
Prepayment Speed (%) 1.00% 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 (%) 0.80% 0.00%
Prepayment Speed (%) 1.00% 0.00%
Severity (%) 95.00% 95.00%
Spreads (%) 4.851% 3.236%
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 $ 36 $ 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]    
Available-for-sale securities 1 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 50 145
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 8 12
Available-for-sale securities 108 248
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 6 201
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Dealer Mark with Inputs [Member] | Subprime private-label securities [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Available-for-sale securities $ 123  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Dealer Mark with Inputs [Member] | Subprime private-label securities [Member] | Available-for-sale securities [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 6.50%  
Prepayment Speed (%) 5.00%  
Severity (%) 85.00%  
Spreads (%) 3.30%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Dealer Mark with Inputs [Member] | Subprime private-label securities [Member] | Available-for-sale securities [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 10.00%  
Prepayment Speed (%) 6.00%  
Severity (%) 95.00%  
Spreads (%) 330.00%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Dealer Mark 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 (%) 8.30%  
Prepayment Speed (%) 5.50%  
Severity (%) 90.00%  
Spreads (%) 3.30%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Dealer Mark without Inputs [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Derivatives $ 212 136
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 1,124 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 $ 149 $ 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 (%) 1.00% 0.50%
Prepayment Speed (%) 3.00% 2.50%
Severity (%) 44.00% 20.00%
Spreads (%) 2.45% 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 (%) 7.00% 5.00%
Prepayment Speed (%) 23.30% 26.00%
Severity (%) 95.00% 89.10%
Spreads (%) 3.10% 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 (%) 3.10% 3.70%
Prepayment Speed (%) 7.30% 6.40%
Severity (%) 70.50% 69.00%
Spreads (%) 2.597% 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 $ 239 $ 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   $ 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%
Prepayment Speed (%)   3.00%
Severity (%)   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 (%)   99.20%
Prepayment Speed (%)   100.00%
Severity (%)   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 (%)   34.80%
Prepayment Speed (%)   10.40%
Severity (%)   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 572 $ 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 164 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 $ 156 $ 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 (%) 0.80% 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 (%) 3.872% 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 (%) 1.94% 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 $ (410) $ (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 (410) (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 (410) (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 (326) (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   $ (149)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Discounted Cash Flow with Inputs [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Long-term Debt, Fair Value $ (125)  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Discounted Cash Flow with Inputs [Member] | Long-term debt [Member] | Minimum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 2.00%  
Prepayment Speed (%) 3.00%  
Severity (%) 58.00%  
Spreads (%) 0.88%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Discounted Cash Flow with Inputs [Member] | Long-term debt [Member] | Maximum [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 7.00%  
Prepayment Speed (%) 100.00%  
Severity (%) 95.00%  
Spreads (%) 3.663%  
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Discounted Cash Flow with Inputs [Member] | Long-term debt [Member] | Weighted Average [Member]    
Fair Value Inputs, Quantitative Information [Line Items]    
Default Rate (%) 4.90%  
Prepayment Speed (%) 92.40%  
Severity (%) 83.00%  
Spreads (%) 2.247%  
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 $ (201) $ (166)