Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Assets and liabilities recorded in our condensed consolidated balance sheets related to mortgage-backed trusts: [Abstract]
Trading, at fair value	$ 38,009	$ 31,504
Available-for-sale, at fair value	22,007	30,654
Other assets	18,674	19,992
Other liabilities	(10,400)	(12,019)
Unconsolidated VIEs [Member] | Mortgage-Backed Trusts [Member]
Assets and liabilities recorded in our condensed consolidated balance sheets related to mortgage-backed trusts: [Abstract]
Trading, at fair value	10,910	11,863
Available-for-sale, at fair value	20,190	27,819
Other assets	102	111
Other liabilities	(755)	(1,440)
Net carrying amount	30,447	38,353
Maximum exposure to loss	36,637	45,311
Total unconsolidated assets	252,211	253,554
Unconsolidated VIEs [Member] | Limited Partnership Investments [Member]
Assets and liabilities recorded in our condensed consolidated balance sheets related to mortgage-backed trusts: [Abstract]
Total unconsolidated assets	4,900	5,800
Fannie Mae Securities [Member]
Assets and liabilities recorded in our condensed consolidated balance sheets related to mortgage-backed trusts: [Abstract]
Trading, at fair value	4,977	4,790
Available-for-sale, at fair value	3,931	5,043
Non-Fannie Mae Securities [Member]
Assets and liabilities recorded in our condensed consolidated balance sheets related to mortgage-backed trusts: [Abstract]
Trading, at fair value	5,933	7,073
Available-for-sale, at fair value	$ 16,259	$ 22,776