Investment Securities (Summary Of Changes In Accumulated OCI For Available-For-Sale Security) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Unrealized Gains and (Losses), Net	$ 464	$ 400
Agency Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning OCI Balance	97	(943)
Unrealized Gains and (Losses), Net	465	396
Reversal of Unrealized (Gains) and Losses, Net on Realization	(1)	4
Ending OCI Balance	$ 561	$ (543)

Accumulated Other Comprehensive Income (Loss) [Roll Forward]

No definition available.

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- Definition

Other Comprehensive Income Reclassification Adjustment For Sale Of Security Reversal Of Prior Period Unrealized Gain And Losses On Realization

+ References

No definition available.

+ Details

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- Definition

Amount, after tax, of accumulated unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e681-108580

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- Definition

Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669646-108580

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e637-108580

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