Income Taxes Deferred Tax Assets and Liabilities (Details) - USD ($)		12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Statutory corporate tax rate	21.00%	35.00%	35.00%	35.00%
Deferred Tax Assets, Operating Loss Carryforwards		$ 0
Deferred Tax Assets, Tax Credit Carryforwards		1,700,000,000
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax		837,000,000
Deferred tax assets:
Mortgage and mortgage-related assets		10,397,000,000	$ 17,130,000,000
Allowance for loan losses and basis in acquired property, net		2,286,000,000	9,496,000,000
Debt and derivative instruments		1,205,000,000	2,989,000,000
Partnership credits		1,695,000,000	1,968,000,000
Partnership and other equity investments		311,000,000	667,000,000
Other, net		1,621,000,000	1,665,000,000
Total deferred tax assets		17,515,000,000	33,915,000,000
Deferred tax liabilities:
Unrealized gains on AFS securities, net		165,000,000	385,000,000
Total deferred tax liabilities		165,000,000	385,000,000
Net deferred tax assets		$ 17,350,000,000	$ 33,530,000,000