Segment Reporting - Segment Earnings and Reconciliation to GAAP Condensed Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net interest Income	$ 3,457	$ 2,410	$ 9,118	$ 8,490
Non-interest income (loss)
Guarantee fee income	315	280	1,161	850
Investment securities gains (losses)	1,122	568	957	(83)
Other income (loss)	172	121	401	247
Benefit (provision) for credit losses	(327)	179	(2,265)	474
Non-interest expense
Administrative expense	(641)	(620)	(1,829)	(1,817)
Credit enhancement expense	(267)	(197)	(731)	(536)
Recoveries	20	0	708	42
REO operations (expense) income	(40)	(58)	(139)	(172)
Other non interest (expense) income	(704)	(547)	(1,821)	(1,696)
Income tax (expense) benefit	(644)	(427)	(1,147)	(1,177)
Net income (loss)	2,463	1,709	4,413	4,622
Changes in unrealized gains (losses) related to available-for-sale securities	(16)	124	576	674
Changes in unrealized gains (losses) related to cash flow hedge relationships	6	19	30	57
Changes in defined benefit plans	(4)	(4)	(10)	(14)
Total other comprehensive income (loss), net of taxes	(14)	139	596	717
Comprehensive income (loss)	2,449	1,848	5,009	5,339
All Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net interest Income	0	0	0	0
Non-interest income (loss)
Guarantee fee income	0	0	0	0
Investment securities gains (losses)	0	0	0	0
Other income (loss)	0	0	0	0
Benefit (provision) for credit losses	0	0	0	0
Non-interest expense
Administrative expense	0	0	0	0
Credit enhancement expense	0	0	0	0
Recoveries	0	0	0	0
REO operations (expense) income	0	0	0	0
Other non interest (expense) income	0	0	0	0
Income tax (expense) benefit	0	0	0	0
Net income (loss)	0	0	0	0
Changes in unrealized gains (losses) related to available-for-sale securities	0	0	0	0
Changes in unrealized gains (losses) related to cash flow hedge relationships	0	0	0	0
Changes in defined benefit plans	0	0	0	0
Total other comprehensive income (loss), net of taxes	0	0	0	0
Comprehensive income (loss)	0	0	0	0
Reclassifications
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net interest Income	3,227	1,621	7,730	5,683
Non-interest income (loss)
Guarantee fee income	(2,671)	(2,078)	(7,301)	(5,598)
Investment securities gains (losses)	(393)	225	(705)	(394)
Other income (loss)	(32)	300	612	577
Benefit (provision) for credit losses	106	99	290	237
Non-interest expense
Administrative expense	0	0	0	0
Credit enhancement expense	156	180	511	517
Recoveries	0	0	0	0
REO operations (expense) income	1	3	3	13
Other non interest (expense) income	(394)	(350)	(1,140)	(1,035)
Income tax (expense) benefit	0	0	0	0
Net income (loss)	0	0	0	0
Changes in unrealized gains (losses) related to available-for-sale securities	0	0	0	0
Changes in unrealized gains (losses) related to cash flow hedge relationships	0	0	0	0
Changes in defined benefit plans	0	0	0	0
Total other comprehensive income (loss), net of taxes	0	0	0	0
Comprehensive income (loss)	0	0	0	0
Single-family Guarantee | Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net interest Income	0	0	0	0
Non-interest income (loss)
Guarantee fee income	2,683	2,064	7,304	5,574
Investment securities gains (losses)	409	377	867	639
Other income (loss)	124	55	56	225
Benefit (provision) for credit losses	(426)	81	(2,400)	240
Non-interest expense
Administrative expense	(409)	(399)	(1,160)	(1,173)
Credit enhancement expense	(416)	(373)	(1,226)	(1,042)
Recoveries	26	0	684	42
REO operations (expense) income	(41)	(61)	(142)	(185)
Other non interest (expense) income	(296)	(180)	(642)	(625)
Income tax (expense) benefit	(343)	(314)	(689)	(750)
Net income (loss)	1,311	1,250	2,652	2,945
Changes in unrealized gains (losses) related to available-for-sale securities	0	0	0	0
Changes in unrealized gains (losses) related to cash flow hedge relationships	0	0	0	0
Changes in defined benefit plans	(3)	(3)	(7)	(9)
Total other comprehensive income (loss), net of taxes	(3)	(3)	(7)	(9)
Comprehensive income (loss)	1,308	1,247	2,645	2,936
Multifamily | Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net interest Income	210	292	707	805
Non-interest income (loss)
Guarantee fee income	303	294	1,158	874
Investment securities gains (losses)	1,091	258	1,001	259
Other income (loss)	43	27	131	84
Benefit (provision) for credit losses	(7)	(1)	(155)	(3)
Non-interest expense
Administrative expense	(128)	(125)	(372)	(357)
Credit enhancement expense	(7)	(4)	(16)	(11)
Recoveries	(6)	0	24	0
REO operations (expense) income	0	0	0	0
Other non interest (expense) income	(9)	(14)	(23)	(27)
Income tax (expense) benefit	(309)	(146)	(507)	(330)
Net income (loss)	1,181	581	1,948	1,294
Changes in unrealized gains (losses) related to available-for-sale securities	(4)	10	119	134
Changes in unrealized gains (losses) related to cash flow hedge relationships	0	0	0	0
Changes in defined benefit plans	0	0	(1)	(2)
Total other comprehensive income (loss), net of taxes	(4)	10	118	132
Comprehensive income (loss)	1,177	591	2,066	1,426
Capital Markets | Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net interest Income	20	497	681	2,002
Non-interest income (loss)
Guarantee fee income	0	0	0	0
Investment securities gains (losses)	15	(292)	(206)	(587)
Other income (loss)	37	(261)	(398)	(639)
Benefit (provision) for credit losses	0	0	0	0
Non-interest expense
Administrative expense	(104)	(96)	(297)	(287)
Credit enhancement expense	0	0	0	0
Recoveries	0	0	0	0
REO operations (expense) income	0	0	0	0
Other non interest (expense) income	(5)	(3)	(16)	(9)
Income tax (expense) benefit	8	33	49	(97)
Net income (loss)	(29)	(122)	(187)	383
Changes in unrealized gains (losses) related to available-for-sale securities	(12)	114	457	540
Changes in unrealized gains (losses) related to cash flow hedge relationships	6	19	30	57
Changes in defined benefit plans	(1)	(1)	(2)	(3)
Total other comprehensive income (loss), net of taxes	(7)	132	485	594
Comprehensive income (loss)	(36)	10	298	977
Operating segments and All Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net interest Income	230	789	1,388	2,807
Non-interest income (loss)
Guarantee fee income	2,986	2,358	8,462	6,448
Investment securities gains (losses)	1,515	343	1,662	311
Other income (loss)	204	(179)	(211)	(330)
Benefit (provision) for credit losses	(433)	80	(2,555)	237
Non-interest expense
Administrative expense	(641)	(620)	(1,829)	(1,817)
Credit enhancement expense	(423)	(377)	(1,242)	(1,053)
Recoveries	20	0	708	42
REO operations (expense) income	(41)	(61)	(142)	(185)
Other non interest (expense) income	(310)	(197)	(681)	(661)
Income tax (expense) benefit	(644)	(427)	(1,147)	(1,177)
Net income (loss)	2,463	1,709	4,413	4,622
Changes in unrealized gains (losses) related to available-for-sale securities	(16)	124	576	674
Changes in unrealized gains (losses) related to cash flow hedge relationships	6	19	30	57
Changes in defined benefit plans	(4)	(4)	(10)	(14)
Total other comprehensive income (loss), net of taxes	(14)	139	596	717
Comprehensive income (loss)	$ 2,449	$ 1,848	$ 5,009	$ 5,339