Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets and liabilities recorded in our consolidated balance sheets:
Trading, at fair value	$ 31,504	$ 30,768
Available-for-sale, at fair value	30,654	38,171
Other assets	19,992	20,231
Other liabilities	(12,019)	(15,441)
Unconsolidated VIEs [Member] | Mortgage-related securities [Member]
Assets and liabilities recorded in our consolidated balance sheets:
Trading, at fair value	11,863	14,219
Available-for-sale, at fair value	27,819	33,307
Other assets	111	119
Other liabilities	(1,440)	(1,668)
Net carrying amount	38,353	45,977
Maximum exposure to loss	45,311	54,148
Total assets of unconsolidated mortgage-backed trusts	253,554	313,202
Unconsolidated VIEs [Member] | Partnership Interest [Member]
Assets and liabilities recorded in our consolidated balance sheets:
Total assets of unconsolidated mortgage-backed trusts	5,800	6,800
Fannie Mae Securities [Member]
Assets and liabilities recorded in our consolidated balance sheets:
Trading, at fair value	4,790	5,660
Available-for-sale, at fair value	5,043	5,866
Non-Fannie Mae Securities [Member]
Assets and liabilities recorded in our consolidated balance sheets:
Trading, at fair value	7,073	8,559
Available-for-sale, at fair value	$ 22,776	$ 27,441