Capital (Restricted Retained Earnings) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Capital [Abstract]
Joint Capital Enhancement Agreement Percentage	20.00%
Percent of Average Balance of Outstanding Consolidated Obligations Prescribed per the Joint Capital Enhancement Agreement for Each Previous Quarter	1.00%
Retained Earnings, Appropriated	$ 504	$ 427

A segregation of retained earnings which is unavailable for dividend distribution. Includes also retained earnings appropriated for loss contingencies.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=65888546&loc=d3e21346-112643

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=65888546&loc=d3e21332-112643

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(23)(a)(4)(i))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-03(30)(a)(3)(ii))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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