Held-to-maturity Securities (Summary of Held-to-Maturity MBS issued by Members or Affliates of Members (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost of held-to-maturity securities	$ 25,864	$ 23,879
Held-to-maturity securities, Gross Unrealized Gains	42	55
Held-to-maturity securities, Gross Unrealized Loss	(60)	(88)
Held-to-maturity securities, fair value	25,846	23,846
M B S Issued by Members or Affiliates of Members [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost of held-to-maturity securities	78	91
Held-to-maturity securities, Gross Unrealized Gains	0	1
Held-to-maturity securities, Gross Unrealized Loss	0	(1)
Held-to-maturity securities, fair value	$ 78	$ 91