Securities - U.S. GSE, Agency, and Treasury Securities (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Fannie Mae
Marketable Securities [Line Items]
Amortized Cost	$ 144,527	$ 130,725
Fair Value	145,423	131,418
Government National Mortgage Association
Marketable Securities [Line Items]
Amortized Cost	102,427	98,278
Fair Value	102,622	98,633
U.S. Treasury
Marketable Securities [Line Items]
Amortized Cost	52,093	28,288
Fair Value	52,485	28,556
Freddie Mac
Marketable Securities [Line Items]
Amortized Cost	37,424	68,481
Fair Value	$ 38,061	$ 68,801