Investments in Securities Trading 1 (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	$ 36,886	$ 40,562
Mortgage-related securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	6,087	8,245
Fannie Mae [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	4,100	4,769
Other agency [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	1,428	2,058
Alt-A and subprime private-label securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	549	636
CMBS [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	9	761
Mortgage revenue bonds [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	1	21
U.S. Treasury securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	$ 30,799	$ 32,317