Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Asset Derivatives [Abstract]
Notional amount	$ 450,981	$ 243,475
Derivative asset, estimated fair value	1,225	271
Netting adjustment	(905)	(1,288)
Derivative Liabilities [Abstract]
Notional amount	288,198	196,666
Derivative liability, estimated fair value	(1,495)	(435)
Netting adjustment	995	1,694
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	658	1,000
Cash collateral received for derivative instruments	568	635
Pay-fixed swap
Asset Derivatives [Abstract]
Notional amount	88,361	41,052
Derivative asset, estimated fair value	0	0
Derivative Liabilities [Abstract]
Notional amount	11,461	29,178
Derivative liability, estimated fair value	(595)	(970)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	92,315	73,579
Derivative asset, estimated fair value	233	816
Derivative Liabilities [Abstract]
Notional amount	33,919	26,382
Derivative liability, estimated fair value	(123)	(62)
Basis swap
Asset Derivatives [Abstract]
Notional amount	250	273
Derivative asset, estimated fair value	192	149
Derivative Liabilities [Abstract]
Notional amount	0	0
Derivative liability, estimated fair value	0	0
Foreign currency swap
Asset Derivatives [Abstract]
Notional amount	237	229
Derivative asset, estimated fair value	57	39
Derivative Liabilities [Abstract]
Notional amount	239	232
Derivative liability, estimated fair value	(58)	(65)
Pay-fixed swaption
Asset Derivatives [Abstract]
Notional amount	5,530	4,600
Derivative asset, estimated fair value	37	18
Derivative Liabilities [Abstract]
Notional amount	2,025	6,375
Derivative liability, estimated fair value	(118)	(219)
Receive-fixed swaption
Asset Derivatives [Abstract]
Notional amount	3,355	2,875
Derivative asset, estimated fair value	346	106
Derivative Liabilities [Abstract]
Notional amount	700	4,600
Derivative liability, estimated fair value	(16)	(232)
Futures
Asset Derivatives [Abstract]
Notional amount	64,398	20,507
Derivative asset, estimated fair value	0	0
Derivative Liabilities [Abstract]
Notional amount	0	0
Derivative liability, estimated fair value	0	0
Risk management derivatives
Asset Derivatives [Abstract]
Notional amount	254,446	143,115
Derivative asset, estimated fair value	865	1,128
Accrued interest receivable	97	226
Netting adjustment	(905)	(1,288)
Total net risk management derivatives - Asset	57	66
Derivative Liabilities [Abstract]
Notional amount	48,344	66,767
Derivative liability, estimated fair value	(910)	(1,548)
Accrued interest payable	(105)	(250)
Netting adjustment	995	1,694
Total net risk management derivatives - Liability	(20)	(104)
Mortgage commitments to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	35,292	7,115
Derivative asset, estimated fair value	145	15
Derivative Liabilities [Abstract]
Notional amount	51	1,787
Derivative liability, estimated fair value	0	(1)
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	144,215	55,531
Derivative asset, estimated fair value	844	137
Derivative Liabilities [Abstract]
Notional amount	607	9,560
Derivative liability, estimated fair value	0	(28)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	199	9,282
Derivative asset, estimated fair value	0	13
Derivative Liabilities [Abstract]
Notional amount	227,828	109,066
Derivative liability, estimated fair value	(1,426)	(277)
Mortgage commitment derivatives
Asset Derivatives [Abstract]
Notional amount	179,706	71,928
Derivative asset, estimated fair value	989	165
Netting adjustment	0	0
Derivative Liabilities [Abstract]
Notional amount	228,486	120,413
Derivative liability, estimated fair value	(1,426)	(306)
Netting adjustment	0	0
Credit enhancement derivatives
Asset Derivatives [Abstract]
Notional amount	16,829	28,432
Derivative asset, estimated fair value	179	40
Derivative Liabilities [Abstract]
Notional amount	11,368	9,486
Derivative liability, estimated fair value	$ (49)	$ (25)

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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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