Investment Securities (Summary of Investment in Agency Security) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Trading and Available-for-sale, Amortized Cost Basis	$ 85,569	$ 57,466
Document Period End Date	Dec. 31, 2018
Debt Securities, Trading and Available-for-sale	$ 84,287	57,080
Total agency MBS, at fair value	82,727	56,168
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Debt Securities, Trading and Available-for-sale, Amortized Cost Basis	264	7
Debt Securities, Trading and Available-for-sale	266	7
Commercial Mortgage Backed Securities [Member]
Debt Securities, Trading and Available-for-sale, Amortized Cost Basis	280	28
Debt Securities, Trading and Available-for-sale	282	29
Credit Risk Transfer Securities [Member]
Debt Securities, Trading and Available-for-sale, Amortized Cost Basis	1,006	834
Debt Securities, Trading and Available-for-sale	1,012	876
Fixed Income Securities [Member] \| Agency Securities [Member]
Debt Securities, Trading and Available-for-sale, Amortized Cost Basis	83,047	55,477
Debt Securities, Trading and Available-for-sale	81,753	55,026
Adjustable-Rate [Member] \| Agency Securities [Member]
Debt Securities, Trading and Available-for-sale, Amortized Cost Basis	212	278
Debt Securities, Trading and Available-for-sale	213	283
Collateralized Mortgage Obligations [Member] \| Agency Securities [Member]
Debt Securities, Trading and Available-for-sale, Amortized Cost Basis	588	629
Debt Securities, Trading and Available-for-sale	583	631
Interest Only And Principal Only Strip [Member] \| Agency Securities [Member]
Debt Securities, Trading and Available-for-sale, Amortized Cost Basis	172	213
Debt Securities, Trading and Available-for-sale	178	228
Agency Securities [Member]
Debt Securities, Trading and Available-for-sale, Amortized Cost Basis	$ 84,019	$ 56,597

Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) at cost.

No definition available.

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- Definition

Represents total investment in agency securities at fair value.

+ References

No definition available.

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- Definition

The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD.

+ References

No definition available.

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- Definition

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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