CostOfSaleOfAvailableForSaleSecuities

No definition available.

Name:	agnc_CostOfSaleOfAvailableForSaleSecuities
Namespace Prefix:	agnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Cost of Sale of Fair Value Option Securities

+ References

No definition available.

+ Details

Name:	agnc_CostofSaleofFairValueOptionSecurities
Namespace Prefix:	agnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Cost of Sale of Investment Securities

+ References

No definition available.

+ Details

Name:	agnc_CostofSaleofInvestmentSecurities
Namespace Prefix:	agnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Net gain (loss) resulting from the sales of securitized, pay-through debt securities collateralized by real estate mortgage loans (mortgages).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13(h))
-URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260

+ Details

Name:	us-gaap_GainLossOnSalesOfMortgageBackedSecuritiesMBS
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

+ References

No definition available.

+ Details

Name:	us-gaap_MarketableSecuritiesRealizedGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow associated with the sale of debt and equity securities classified as 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 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26853-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=us-gaap_AvailableforsaleSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=agnc_SecuritiesRemeasuredatFairValueMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_UnderlyingAssetClassAxis=us-gaap_SecuritiesAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=agnc_CostandProceedsofInvestmentSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=agnc_GrossGainLossofInvestmentSecuritiesMember
Namespace Prefix:
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Investment Securities (Summary Of Net Gain From Sale Of Agency Securities) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cost of Sale of Fair Value Option Securities									$ (5,344)	$ (12,913)	$ 0
Cost of Sale of Investment Securities									(9,650)	(19,237)	(17,907)
Proceeds from agency MBS sold									21,308	14,557	10,393
Net gain (loss) on sale of investment securities	$ (21)	$ (40)	$ (74)	$ (2)	$ (16)	$ 22	$ 15	$ (84)	(137)	(63)	109
Available-for-sale Securities [Member]
Agency MBS sold, at cost									(4,306)	(6,324)	(17,907)
Proceeds from agency MBS sold									4,227	6,241	18,016
Net gain (loss) on sale of investment securities										(83)	109
Gross gain on sale of investment securities									6	16	123
Gross loss on sale of investment securities									(85)	(99)	(14)
Securities Remeasured at Fair Value [Member]
Proceeds from agency MBS sold									5,286	12,933	0
Net gain (loss) on sale of investment securities										20	0
Gross gain on sale of investment securities									16	48	0
Gross loss on sale of investment securities									(74)	(28)	0
Securities (Assets) [Member]
Proceeds from agency MBS sold									9,513	19,174	18,016
Net gain (loss) on sale of investment securities									(137)	(63)	109
Gross gain on sale of investment securities									22	64	123
Gross loss on sale of investment securities									(159)	$ (127)	$ (14)
Cost and Proceeds of Investment Securities [Member] \| Available-for-sale Securities [Member]
Net gain (loss) on sale of investment securities									(79)
Cost and Proceeds of Investment Securities [Member] \| Securities Remeasured at Fair Value [Member]
Net gain (loss) on sale of investment securities									(58)
Gross Gain & Loss of Investment Securities [Member] \| Available-for-sale Securities [Member]
Net gain (loss) on sale of investment securities									(79)
Gross Gain & Loss of Investment Securities [Member] \| Securities Remeasured at Fair Value [Member]
Net gain (loss) on sale of investment securities									$ (58)