Pledged Assets, Collateral Type and Contractual Maturities of Repurchase Agreements and Securities Lending Agreements (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Secured Borrowings, Gross Including Not Subject to Master Netting Arrangement [Abstract]
Repurchase agreements	$ 48,871	$ 106,169
Securities lending	6,017	4,869
Total repurchases and securities lending	54,888	111,038
Overnight/continuous [Member]
Secured Borrowings, Gross Including Not Subject to Master Netting Arrangement [Abstract]
Repurchase agreements	37,173	79,793
Securities lending	5,467	4,724
Total repurchases and securities lending	42,640	84,517
Up to 30 days [Member]
Secured Borrowings, Gross Including Not Subject to Master Netting Arrangement [Abstract]
Repurchase agreements	1,963	17,681
Securities lending	0	0
Total repurchases and securities lending	1,963	17,681
30-90 days [Member]
Secured Borrowings, Gross Including Not Subject to Master Netting Arrangement [Abstract]
Repurchase agreements	6,150	4,825
Securities lending	550	145
Total repurchases and securities lending	6,700	4,970
Over 90 days [Member]
Secured Borrowings, Gross Including Not Subject to Master Netting Arrangement [Abstract]
Repurchase agreements	3,585	3,870
Securities lending	0	0
Total repurchases and securities lending	3,585	3,870
Securities of U.S. Treasury and federal agencies [Member]
Secured Borrowings, Gross Including Not Subject to Master Netting Arrangement [Abstract]
Repurchase agreements	22,342	48,161
Securities lending	57	163
Securities of U.S. states and political subdivisions [Member]
Secured Borrowings, Gross Including Not Subject to Master Netting Arrangement [Abstract]
Repurchase agreements	46	104
Federal agencies [Member]
Secured Borrowings, Gross Including Not Subject to Master Netting Arrangement [Abstract]
Repurchase agreements	13,184	44,737
Securities lending	42	0
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Secured Borrowings, Gross Including Not Subject to Master Netting Arrangement [Abstract]
Repurchase agreements	1,176	1,818
Corporate debt securities [Member]
Secured Borrowings, Gross Including Not Subject to Master Netting Arrangement [Abstract]
Repurchase agreements	8,780	7,126
Securities lending	98	223
Asset-backed securities [Member]
Secured Borrowings, Gross Including Not Subject to Master Netting Arrangement [Abstract]
Repurchase agreements	1,050	1,844
Equity securities [Member]
Secured Borrowings, Gross Including Not Subject to Master Netting Arrangement [Abstract]
Repurchase agreements	1,463	1,674
Securities lending	5,788	4,481
Other [Member]
Secured Borrowings, Gross Including Not Subject to Master Netting Arrangement [Abstract]
Repurchase agreements	830	705
Securities lending	$ 32	$ 2

Amount, before effects of master netting arrangements, of funds outstanding borrowed in the form of a financial asset repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same financial asset at a date certain for a specified price. Includes repurchase-to-maturity transactions and liabilities not subject to a master netting arrangement.

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- Definition

Amount, before effects of master netting arrangements, of financial assets loaned to entities in exchange for collateral and funds outstanding borrowed in the form of a financial asset repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same financial assets at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 7
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL34722452-111729

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 7
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL34722452-111729

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL34722452-111729

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- References

No definition available.

+ Details

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- Definition

Amount, before effects of master netting arrangements, of financial assets loaned to entities in exchange for collateral. Includes liabilities not subject to a master netting arrangement and financial assets transferred other than securities that qualify as secured borrowings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 7
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL34722452-111729

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 7
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL34722452-111729

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