Income Taxes Deferred Tax Assets and Liabilities (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Deferred Tax Assets, Operating Loss Carryforwards	$ 0
Deferred Tax Assets, Tax Credit Carryforwards	2,000,000,000
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	302,000,000
Deferred tax assets:
Mortgage and mortgage-related assets	17,130,000,000	$ 16,956,000,000
Allowance for loan losses and basis in acquired property, net	9,496,000,000	11,760,000,000
Debt and derivative instruments	2,989,000,000	3,512,000,000
Partnership credits	1,968,000,000	3,402,000,000
Partnership and other equity investments	667,000,000	745,000,000
Other, net	1,665,000,000	1,543,000,000
Total deferred tax assets	33,915,000,000	37,918,000,000
Deferred tax liabilities:
Unrealized gains on AFS securities, net	385,000,000	731,000,000
Total deferred tax liabilities	385,000,000	731,000,000
Net deferred tax assets	$ 33,530,000,000	$ 37,187,000,000