Investments in Securities Trading 1 (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	$ 37,684	$ 40,562
Mortgage-related securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	7,529	8,245
Fannie Mae [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	4,594	4,769
Other agency [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	2,053	2,058
Alt-A and subprime private-label securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	624	636
CMBS [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	238	761
Mortgage revenue bonds [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	20	21
U.S. Treasury securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	$ 30,155	$ 32,317