Mortgage Loans Held for Portfolio (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
MPF Program Percent	98.00%	98.00%
MPP Program Percent	2.00%	2.00%
US Government Agency Insured Loans [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Allowance for Credit Loss	$ 0	$ 0
Real Estate Loan [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Accrued Interest, after Allowance for Credit Loss	$ 49	$ 48