Capital and Mandatorily Redeemable Capital Stock (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Capital [Abstract]
Redemption Period For Excess Capital Stock	5 years
Mandatorily redeemable capital stock	$ 1	$ 1	$ 1	$ 2	$ 3	$ 1

Amount that would be paid, determined under the conditions specified in the contract, if the holder of the share has the right to redeem the shares.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109262807&loc=d3e22047-110879

Name:	us-gaap_SharesSubjectToMandatoryRedemptionSettlementTermsAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant