Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Asset Derivatives [Abstract]
Notional amount	$ 512,313	$ 243,475
Derivative asset, estimated fair value	1,038	271
Netting adjustment	(2,037)	(1,288)
Liability Derivatives [Abstract]
Notional amount	340,487	196,666
Derivative liability, estimated fair value	(965)	(435)
Netting adjustment	2,053	1,694
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	991	1,000
Cash collateral received for derivative instruments	975	635
Pay-fixed Swap
Asset Derivatives [Abstract]
Notional amount	110,215	41,052
Derivative asset, estimated fair value	0	0
Liability Derivatives [Abstract]
Notional amount	25,728	29,178
Derivative liability, estimated fair value	(1,297)	(970)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	109,774	73,579
Derivative asset, estimated fair value	1,082	816
Liability Derivatives [Abstract]
Notional amount	19,213	26,382
Derivative liability, estimated fair value	(54)	(62)
Basis Swap
Asset Derivatives [Abstract]
Notional amount	250	273
Derivative asset, estimated fair value	218	149
Liability Derivatives [Abstract]
Notional amount	0	0
Derivative liability, estimated fair value	0	0
Foreign Currency Swap
Asset Derivatives [Abstract]
Notional amount	224	229
Derivative asset, estimated fair value	41	39
Liability Derivatives [Abstract]
Notional amount	226	232
Derivative liability, estimated fair value	(78)	(65)
Pay-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	5,400	4,600
Derivative asset, estimated fair value	10	18
Liability Derivatives [Abstract]
Notional amount	5,525	6,375
Derivative liability, estimated fair value	(341)	(219)
Receive-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	6,625	2,875
Derivative asset, estimated fair value	591	106
Liability Derivatives [Abstract]
Notional amount	800	4,600
Derivative liability, estimated fair value	(138)	(232)
Future [Member]
Asset Derivatives [Abstract]
Notional amount	55,004	20,507
Derivative asset, estimated fair value	0	0
Liability Derivatives [Abstract]
Notional amount	0	0
Derivative liability, estimated fair value	0	0
Risk Management Derivatives
Asset Derivatives [Abstract]
Notional amount	287,492	143,115
Derivative asset, estimated fair value	1,942	1,128
Accrued interest receivable (payable)	111	226
Netting adjustment	(2,037)	(1,288)
Total net risk management derivatives	16	66
Liability Derivatives [Abstract]
Notional amount	51,492	66,767
Derivative liability, estimated fair value	(1,908)	(1,548)
Accrued interest receivable (payable)	(230)	(250)
Netting adjustment	2,053	1,694
Total net risk management derivatives	(85)	(104)
Mortgage commitments to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	36,756	7,115
Derivative asset, estimated fair value	93	15
Liability Derivatives [Abstract]
Notional amount	9,180	1,787
Derivative liability, estimated fair value	(13)	(1)
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	122,096	55,531
Derivative asset, estimated fair value	402	137
Liability Derivatives [Abstract]
Notional amount	37,607	9,560
Derivative liability, estimated fair value	(70)	(28)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	45,165	9,282
Derivative asset, estimated fair value	68	13
Liability Derivatives [Abstract]
Notional amount	232,148	109,066
Derivative liability, estimated fair value	(759)	(277)
Mortgage commitment derivatives
Asset Derivatives [Abstract]
Notional amount	204,017	71,928
Derivative asset, estimated fair value	563	165
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	278,935	120,413
Derivative liability, estimated fair value	(842)	(306)
Netting adjustment	0	0
Other
Asset Derivatives [Abstract]
Notional amount	20,804	28,432
Derivative asset, estimated fair value	459	40
Liability Derivatives [Abstract]
Notional amount	10,060	9,486
Derivative liability, estimated fair value	$ (38)	$ (25)

Represents carrying amount of interest earned on derivative assets but not received, as of the balance sheet date.

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Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position. Includes all derivative assets subject to and not subject to master netting arrangements.

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Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position. Includes all derivatives liability subject and not subject to master netting arrangements.

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Represents carrying value of accrued interest payable on derivative liabilities that has been incurred and is unpaid, as of the balance sheet date.

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Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

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Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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Nominal or face amount used to calculate payments on the derivative asset.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Amount of right to receive cash collateral under master netting arrangements offset against derivative liabilities.

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Fair value of asset associated with financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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Nominal or face amount used to calculate payments on the derivative liability.

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