Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Asset Derivatives [Abstract]
Notional amount	$ 392,994	$ 243,475
Derivative asset, estimated fair value	2,771	271
Netting adjustment	(2,137)	(1,288)
Liability Derivatives [Abstract]
Notional amount	256,812	196,666
Derivative liability, estimated fair value	(3,809)	(435)
Netting adjustment	2,607	1,694
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	1,400	1,000
Cash collateral received for derivative instruments	896	635
Pay-fixed Swap
Asset Derivatives [Abstract]
Notional amount	50,946	41,052
Derivative asset, estimated fair value	0	0
Liability Derivatives [Abstract]
Notional amount	29,603	29,178
Derivative liability, estimated fair value	(1,930)	(970)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	94,704	73,579
Derivative asset, estimated fair value	1,151	816
Liability Derivatives [Abstract]
Notional amount	9,854	26,382
Derivative liability, estimated fair value	(2)	(62)
Basis Swap
Asset Derivatives [Abstract]
Notional amount	273	273
Derivative asset, estimated fair value	205	149
Liability Derivatives [Abstract]
Notional amount	0	0
Derivative liability, estimated fair value	0	0
Foreign Currency Swap
Asset Derivatives [Abstract]
Notional amount	215	229
Derivative asset, estimated fair value	29	39
Liability Derivatives [Abstract]
Notional amount	217	232
Derivative liability, estimated fair value	(93)	(65)
Pay-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	4,600	4,600
Derivative asset, estimated fair value	7	18
Liability Derivatives [Abstract]
Notional amount	5,875	6,375
Derivative liability, estimated fair value	(328)	(219)
Receive-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	6,625	2,875
Derivative asset, estimated fair value	619	106
Liability Derivatives [Abstract]
Notional amount	350	4,600
Derivative liability, estimated fair value	(130)	(232)
Future [Member]
Asset Derivatives [Abstract]
Notional amount	53,742	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	211,105	143,115
Derivative asset, estimated fair value	2,011	1,128
Accrued interest receivable (payable)	195	226
Netting adjustment	(2,137)	(1,288)
Total net risk management derivatives	69	66
Liability Derivatives [Abstract]
Notional amount	45,899	66,767
Derivative liability, estimated fair value	(2,483)	(1,548)
Accrued interest receivable (payable)	(310)	(250)
Netting adjustment	2,607	1,694
Total net risk management derivatives	(186)	(104)
Mortgage commitments to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	31,152	7,115
Derivative asset, estimated fair value	413	15
Liability Derivatives [Abstract]
Notional amount	10,452	1,787
Derivative liability, estimated fair value	(56)	(1)
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	103,770	55,531
Derivative asset, estimated fair value	2,153	137
Liability Derivatives [Abstract]
Notional amount	10,936	9,560
Derivative liability, estimated fair value	(36)	(28)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	20,070	9,282
Derivative asset, estimated fair value	99	13
Liability Derivatives [Abstract]
Notional amount	177,213	109,066
Derivative liability, estimated fair value	(3,502)	(277)
Mortgage commitment derivatives
Asset Derivatives [Abstract]
Notional amount	154,992	71,928
Derivative asset, estimated fair value	2,665	165
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	198,601	120,413
Derivative liability, estimated fair value	(3,594)	(306)
Netting adjustment	0	0
Other
Asset Derivatives [Abstract]
Notional amount	26,897	28,432
Derivative asset, estimated fair value	37	40
Liability Derivatives [Abstract]
Notional amount	12,312	9,486
Derivative liability, estimated fair value	$ (29)	$ (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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