Investment Securities (Details 1) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Available-for-sale investment securities with gross unrealized losses and length of time
Estimated Fair Value, Less than 12 months	$ 0	$ 224
Estimated Fair Value, 12 months or more	477	873
Available For Sale Securities Continuous Unrealized Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 Months	0	(2)
Gross Unrealized Losses, 12 months or more	(3)	(16)
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale investment securities with gross unrealized losses and length of time
Estimated Fair Value, Less than 12 months	0	0
Estimated Fair Value, 12 months or more	0	82
Available For Sale Securities Continuous Unrealized Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 Months	0	0
Gross Unrealized Losses, 12 months or more	0	(1)
US Treasury Securities [Member]
Available-for-sale investment securities with gross unrealized losses and length of time
Estimated Fair Value, Less than 12 months	0	224
Estimated Fair Value, 12 months or more	477	791
Available For Sale Securities Continuous Unrealized Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 Months	0	(2)
Gross Unrealized Losses, 12 months or more	$ (3)	$ (15)

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Debt Securities, Available-for-sale, Unrealized Loss Position1 [Abstract]

+ References

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922890-210455

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27337-111563

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-Section 55
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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