Held-to-maturity Securities (Held-to-maturity by Major Security Type) (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
State or local housing agency debt obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost of held-to-maturity securities	1	1
Held-to-maturity securities, Gross Unrealized Gains	0	0
Held-to-maturity securities, Gross Unrealized Loss	0	0
Held-to-maturity securities, fair value	1	1
Government-Sponsored Enterprises Debt Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost of held-to-maturity securities	4,172	2,672
Held-to-maturity securities, Gross Unrealized Gains	5	5
Held-to-maturity securities, Gross Unrealized Loss	(1)	(2)
Held-to-maturity securities, fair value	4,176	2,675
Mortgage-backed Securities, Private-label residential[Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost of held-to-maturity securities	357	416
Held-to-maturity securities, Gross Unrealized Gains	4	4
Held-to-maturity securities, Gross Unrealized Loss	(1)	(2)
Held-to-maturity securities, fair value	360	418
Residential [Member] \| U.S. agency obligations-guaranteed residential
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost of held-to-maturity securities	104	118
Held-to-maturity securities, Gross Unrealized Gains	0	2
Held-to-maturity securities, Gross Unrealized Loss	0	0
Held-to-maturity securities, fair value	104	120
Residential [Member] \| Government-sponsored enterprises
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost of held-to-maturity securities	9,558	9,304
Held-to-maturity securities, Gross Unrealized Gains	32	40
Held-to-maturity securities, Gross Unrealized Loss	(30)	(43)
Held-to-maturity securities, fair value	9,560	9,301
Commercial [Member] \| Government-sponsored enterprises
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost of held-to-maturity securities	11,672	11,368
Held-to-maturity securities, Gross Unrealized Gains	1	4
Held-to-maturity securities, Gross Unrealized Loss	(28)	(41)
Held-to-maturity securities, fair value	$ 11,645	$ 11,331

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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- Definition

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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