Capital and Mandatorily Redeemable Capital Stock (Mandatorily Redeemable Capital Stock Roll-forward) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Capital [Abstract]
Balance, beginning of period	$ 1	$ 3	$ 1	$ 1
Net Shares Reclassified to Mandatorily Redeemable Capital Stock	0	1	0	33
Repurchase/redemption of mandatorily redeemable capital stock	0	(2)	0	(32)
Balance, end of period	$ 1	$ 2	$ 1	$ 2