Fair Value Level 3 Valuation Inputs (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	$ 11,013	$ 12,057
Derivatives	261	654
Fannie Mae [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt, fair value	(8,491)	(9,582)
Consolidated Trusts [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt, fair value	(32,760)	(36,524)
Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	36,886	40,562
Available-for-sale securities	5,963	8,363
Mortgage loans held for investment, at fair value	11,013	12,057
Long-term debt, fair value	(41,251)	(46,106)
Recurring Fair Value Measurements [Member] | Fannie Mae [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt, fair value	(8,491)	(9,582)
Recurring Fair Value Measurements [Member] | Fannie Mae [Member] | Senior floating [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt, fair value	(8,491)	(9,582)
Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt, fair value	(32,760)	(36,524)
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	3,947	7,118
Available-for-sale securities	4,468	6,210
Mortgage loans held for investment, at fair value	2,869,318	2,767,813
Mortgage loans held-for-sale, at lower of cost or fair value	2,389	509
Significant Other Observable Inputs (Level 2) [Member] | Fannie Mae [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt, fair value	(265,390)	(298,980)
Significant Other Observable Inputs (Level 2) [Member] | Consolidated Trusts [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt, fair value	(2,995,046)	(2,901,316)
Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	3,947	7,118
Available-for-sale securities	4,468	6,210
Mortgage loans held for investment, at fair value	9,923	10,860
Long-term debt, fair value	(40,177)	(45,518)
Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member] | Fannie Mae [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt, fair value	(8,122)	(9,235)
Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member] | Fannie Mae [Member] | Senior floating [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt, fair value	(8,122)	(9,235)
Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt, fair value	(32,055)	(36,283)
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held-for-sale, at lower of cost or fair value	149	250
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	2,140	1,127
Available-for-sale securities	1,495	2,153
Mortgage loans held for investment, at fair value	318,453	316,742
Mortgage loans held-for-sale, at lower of cost or fair value	2,780	2,751
Significant Unobservable Inputs (Level 3) [Member] | Fannie Mae [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt, fair value	(824)	(770)
Significant Unobservable Inputs (Level 3) [Member] | Consolidated Trusts [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt, fair value	(40,075)	(36,668)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	2,140	1,127
Available-for-sale securities	1,495	2,153
Mortgage loans held for investment, at fair value	1,090	1,197
Derivatives	125	44
Long-term debt, fair value	(1,074)	(588)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Various Valuation Technique without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Derivatives	6	(76)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Derivatives		21
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Dealer Mark [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Derivatives	119	89
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Internal Model [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Derivatives		10
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	930	1,034
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	$ 100
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 (%)	1.70%
Prepayment Speed (%)	3.30%
Severity (%)	38.00%
Spreads (%)	1.137%
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 (%)	8.40%
Prepayment Speed (%)	16.50%
Severity (%)	95.00%
Spreads (%)	1.40%
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 (%)	3.30%
Prepayment Speed (%)	11.40%
Severity (%)	72.30%
Spreads (%)	1.297%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-family [Member] | Various Valuation Technique without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	$ 96	218
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	300	300
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	434	516
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	$ 160	$ 163
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 (%)	0.45%	0.55%
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 (%)	2.862%	3.052%
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 (%)	1.243%	1.402%
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	$ (369)	$ (347)
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	(369)	(347)
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	(369)	(347)
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	(705)	(241)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Various Valuation Technique without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt, fair value	(205)	(241)
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	$ (500)
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 (%)	2.40%
Prepayment Speed (%)	5.10%
Severity (%)	29.00%
Spreads (%)	0.40%
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 (%)	5.90%
Prepayment Speed (%)	100.00%
Severity (%)	69.00%
Spreads (%)	2.393%
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 (%)	4.60%
Prepayment Speed (%)	99.50%
Severity (%)	56.40%
Spreads (%)	0.88%
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held-for-sale, at lower of cost or fair value	$ 2,324	1,088
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Single Vendor Without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held-for-sale, at lower of cost or fair value	89	54
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Various Valuation Technique without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held-for-sale, at lower of cost or fair value	0	9
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Consensus Without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held-for-sale, at lower of cost or fair value	2,235	1,025
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Single-family [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	1,309	1,792
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Single-family [Member] | Various Valuation Technique without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	161	99
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Single-family [Member] | Internal Model [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	1,846	2,816
Acquired property, net	308	476
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Single-family [Member] | Accepted Offers [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	221	340
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Single-family [Member] | Appraisals [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	429	571
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Single-family [Member] | Walk Forwards [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	190	306
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Multifamily [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	167	198
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Multifamily [Member] | Various Valuation Technique without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	4	3
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Multifamily [Member] | Broker Price Opinions [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	24	25
Acquired property, net	29	0
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Nonrecurring [Member] | Multifamily [Member] | Asset Manager Estimate [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	139	170
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	1,886	835
Available-for-sale securities		235
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	$ 902
Available-for-sale securities		$ 129
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Trading securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)	0.00%
Spreads (%)	0.478%
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Trading securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)	188.00%
Spreads (%)	3.95%
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Trading securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)	163.20%
Spreads (%)	2.016%
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Available-for-sale securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)		124.80%
Spreads (%)		1.75%
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Available-for-sale securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)		165.50%
Spreads (%)		2.10%
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Available-for-sale securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)		142.40%
Spreads (%)		1.825%
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	$ 943
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Trading securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)	177.00%
Spreads (%)	1.50%
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Trading securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)	177.00%
Spreads (%)	1.50%
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Trading securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)	177.00%
Spreads (%)	1.50%
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Various Valuation Technique without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	$ 41	$ 26
Available-for-sale securities	196	34
Agency | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus Without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities		809
Available-for-sale securities		72
Alt-A and subprime private-label securities [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	549	636
Available-for-sale securities	2,034	2,709
Alt-A and subprime private-label securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	296	365
Available-for-sale securities	1,854	2,492
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	253	271
Available-for-sale securities	180	217
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities		$ 93
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Available-for-sale securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		2.50%
Prepayment Speed (%)		3.00%
Severity (%)		38.00%
Spreads (%)		2.661%
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Available-for-sale securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		8.00%
Prepayment Speed (%)		11.00%
Severity (%)		80.00%
Spreads (%)		3.068%
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Available-for-sale securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		3.80%
Prepayment Speed (%)		4.90%
Severity (%)		48.10%
Spreads (%)		2.971%
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities		$ 232
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Trading securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		0.40%
Prepayment Speed (%)		4.30%
Severity (%)		71.00%
Spreads (%)		2.446%
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Trading securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		10.90%
Prepayment Speed (%)		7.40%
Severity (%)		95.00%
Spreads (%)		2.539%
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Trading securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		8.20%
Prepayment Speed (%)		6.60%
Severity (%)		88.90%
Spreads (%)		2.515%
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Various Valuation Technique without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	97
Available-for-sale securities	180
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus Without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	156	$ 39
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities		$ 45
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)		3.61%
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)		4.50%
Alt-A and subprime private-label securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)		4.06%
Mortgage revenue bonds [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	1	$ 21
Available-for-sale securities	749	1,272
Mortgage revenue bonds [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	0	0
Available-for-sale securities	0	0
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	1	21
Available-for-sale securities	749	1,272
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	$ 594	$ 684
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Available-for-sale securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)	0.025%	(0.168%)
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Available-for-sale securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)	3.605%	3.369%
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor With Inputs [Member] | Available-for-sale securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)	0.60%	0.443%
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single Vendor Without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities		$ 126
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Various Valuation Technique without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	$ 1	2
Available-for-sale securities	155	27
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities		19
Available-for-sale securities		$ 435
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Trading securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)		0.13%
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Trading securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)		2.682%
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Trading securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)		2.522%
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)		(0.168%)
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)		3.911%
Mortgage revenue bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spreads (%)		2.60%
Other [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	399	$ 462
Other [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	29	33
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	370	429
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities		$ 47
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Available-for-sale securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		0.50%
Prepayment Speed (%)		2.50%
Severity (%)		20.00%
Spreads (%)		2.216%
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Available-for-sale securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		3.50%
Prepayment Speed (%)		6.00%
Severity (%)		88.00%
Spreads (%)		3.002%
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with Inputs [Member] | Available-for-sale securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		3.50%
Prepayment Speed (%)		2.50%
Severity (%)		87.50%
Spreads (%)		2.377%
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Various Valuation Technique without Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	40	$ 34
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	$ 330	$ 348
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)	1.60%	2.30%
Prepayment Speed (%)	0.50%	0.50%
Severity (%)	50.00%	95.00%
Spreads (%)	1.029%	1.90%
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)	3.50%	2.30%
Prepayment Speed (%)	2.50%	0.50%
Severity (%)	100.00%	95.00%
Spreads (%)	6.08%	4.50%
Other [Member] | Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted Cash Flow with Inputs [Member] | Available-for-sale securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)	3.40%	2.30%
Prepayment Speed (%)	2.40%	0.50%
Severity (%)	98.10%	95.00%
Spreads (%)	5.799%	4.491%