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Mortgage-Backed Securities Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Catch-up Premium Amortization Adjustment	$ (0.7)	$ (0.9)
Available-for-sale Securities, Gross Unrealized Loss	(4.2)
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ (2.1)
Other-than-temporary Impairment Loss, Debt Securities, Portion Recognized in Earnings		$ (1.1)

X

- Definition

For securities whose cash flows vary depending on prepayments, an effective yield retroactive to the time of purchase is periodically recomputed based on actual prepayments and changes in projected prepayment activity, and a catch-up adjustment, or "Catch-up Premium Amortization Adjustment," is made to amortization to reflect the cumulative impact of the change in effective yield.

+ References

No definition available.

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X

- Definition

Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

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- Definition

Amount of allowance for credit 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/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922900-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-Section 50
-Paragraph 9
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-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922900-210455

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

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- References

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- Definition

Amount of other-than-temporary impairment (OTTI) on investment in debt security, recognized in earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 8A
-URI http://asc.fasb.org/extlink&oid=118954083&loc=SL6284422-111562

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