Held-to-Maturity Securities (Major Security Types) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 2,370	$ 2,992
Gross Unrealized Gains	77	53
Gross Unrealized Losses	(8)	(24)
Fair Value	2,439	3,021
GSE Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	384	389
Gross Unrealized Gains	72	48
Gross Unrealized Losses	0	(2)
Fair Value	456	435
State or Local Housing Agency Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	221	391
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(1)	(1)
Fair Value	221	391
Non-Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	605	780
Gross Unrealized Gains	73	49
Gross Unrealized Losses	(1)	(3)
Fair Value	677	826
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,765	2,212
Gross Unrealized Gains	4	4
Gross Unrealized Losses	(7)	(21)
Fair Value	1,762	2,195
Single Family [Member] \| U.S. Obligations MBS [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	5	9
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	5	9
Single Family [Member] \| GSE MBS [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,752	2,192
Gross Unrealized Gains	4	4
Gross Unrealized Losses	(7)	(21)
Fair Value	1,749	2,175
Commercial Mortgage Backed Securities [Member] \| U.S. Obligations MBS [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1	1
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	1	1
Residential Mortgage Backed Securities [Member] \| Private-Label MBS [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	7	10
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 7	$ 10

Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

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Amount, before other-than-temporary impairment (OTTI) accretion, of investment in debt securities measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

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