Investments in Securities Trading 1 (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	$ 43,901	$ 34,679
Mortgage-related securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	6,479	5,457
Fannie Mae [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	1,469	3,876
Other agency [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	3,642	1,118
Alt-A and subprime private-label securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	1,367	453
CMBS [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	0	9
Mortgage revenue bonds [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	1	1
Non-mortgage-related securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	37,422	29,222
U.S. Treasury securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	37,328	29,222
Other securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	$ 94	$ 0