Investments in Securities Trading 1 (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	$ 39,274	$ 40,562
Mortgage-related securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	6,856	8,245
Fannie Mae [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	4,277	4,769
Other agency [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	1,969	2,058
Alt-A and subprime private-label securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	593	636
CMBS [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	16	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	$ 32,418	$ 32,317