Investments in Securities - Trading 1 (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	$ 97,209	$ 136,542
Mortgage-related securities
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	4,997	6,013
Fannie Mae
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	1,715	2,404
Other agency
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	3,139	3,451
Private-label and other mortgage securities
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	143	158
Total non-mortgage-related securities
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	92,212	130,529
U.S. Treasury securities
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	92,192	130,456
Other securities
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	20	73
Consolidated trusts
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	$ 642	$ 793