Mortgage Loans Held for Portfolio (Details 2) - USD ($) $ in Millions		Jun. 30, 2017	Dec. 31, 2016
Union Savings Bank [Member]
Participating Mortgage Loans [Line Items]
Unpaid Principal Balances Greater Than Five Percent of Total		$ 3,118	$ 2,886
Percent of Total		34.00%	32.00%
Guardian Saving Bank FSB [Member]
Participating Mortgage Loans [Line Items]
Unpaid Principal Balances Greater Than Five Percent of Total		$ 895	$ 855
Percent of Total		10.00%	10.00%
PNC Bank, N.A. [Member]
Participating Mortgage Loans [Line Items]
Unpaid Principal Balances Greater Than Five Percent of Total	[1]	$ 583	$ 660
Percent of Total	[1]	6.00%	7.00%

[1] Former member.