Securities - U.S. GSE, Agency, and Treasury Securities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Marketable Securities [Line Items]
Amortized Cost	$ 369,668	$ 330,440
Fair Value	366,939	321,225
Fannie Mae
Marketable Securities [Line Items]
Amortized Cost	127,610	123,813
Fair Value	126,061	118,708
Government National Mortgage Association
Marketable Securities [Line Items]
Amortized Cost	101,052	118,700
Fair Value	99,757	115,314
U.S. Treasury
Marketable Securities [Line Items]
Amortized Cost	58,263	10,533
Fair Value	58,208	10,428
Freddie Mac
Marketable Securities [Line Items]
Amortized Cost	25,717	24,908
Fair Value	$ 25,553	$ 24,075