Investments in Securities Trading 1 (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	$ 40,097	$ 34,679
Mortgage-related securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	6,840	5,457
Fannie Mae [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	1,739	3,876
Other agency [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	2,347	1,118
Alt-A and subprime private-label securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	2,745	453
CMBS [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	8	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	33,257	29,222
U.S. Treasury securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	33,160	29,222
Other securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	$ 97	$ 0