Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Asset Derivatives [Abstract]
Notional amount	$ 266,935	$ 178,138
Derivative asset, estimated fair value	458	171
Netting adjustment	(2,266)	(4,272)
Derivative Liabilities [Abstract]
Notional amount	161,488	338,089
Derivative liability, estimated fair value	(777)	(328)
Netting adjustment	2,315	4,979
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	713	1,400
Cash collateral received for derivative instruments	664	649
Pay-fixed swap
Asset Derivatives [Abstract]
Notional amount	71,416	52,732
Derivative asset, estimated fair value	438	772
Derivative Liabilities [Abstract]
Notional amount	21,253	70,211
Derivative liability, estimated fair value	(740)	(2,120)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	88,799	31,671
Derivative asset, estimated fair value	1,113	2,391
Derivative Liabilities [Abstract]
Notional amount	58,399	138,852
Derivative liability, estimated fair value	(860)	(1,764)
Basis swap
Asset Derivatives [Abstract]
Notional amount	250	873
Derivative asset, estimated fair value	104	124
Derivative Liabilities [Abstract]
Notional amount	624	0
Derivative liability, estimated fair value	0	0
Foreign currency swap
Asset Derivatives [Abstract]
Notional amount	221	234
Derivative asset, estimated fair value	22	59
Derivative Liabilities [Abstract]
Notional amount	223	236
Derivative liability, estimated fair value	(72)	(56)
Pay-fixed swaption
Asset Derivatives [Abstract]
Notional amount	10,375	9,750
Derivative asset, estimated fair value	191	95
Derivative Liabilities [Abstract]
Notional amount	1,000	4,000
Derivative liability, estimated fair value	(4)	(20)
Receive-fixed swaption
Asset Derivatives [Abstract]
Notional amount	500	250
Derivative asset, estimated fair value	20	13
Derivative Liabilities [Abstract]
Notional amount	7,375	9,250
Derivative liability, estimated fair value	(338)	(304)
Future [Member]
Asset Derivatives [Abstract]
Notional amount	16,631	0
Derivative asset, estimated fair value	0	0
Derivative Liabilities [Abstract]
Notional amount	0	7,315
Derivative liability, estimated fair value	0	0
Risk management derivatives
Asset Derivatives [Abstract]
Notional amount	188,192	95,510
Derivative asset, estimated fair value	1,888	3,454
Accrued interest receivable	400	835
Netting adjustment	(2,266)	(4,272)
Total net risk management derivatives - Asset	22	17
Derivative Liabilities [Abstract]
Notional amount	88,874	229,864
Derivative liability, estimated fair value	(2,014)	(4,264)
Accrued interest payable	(419)	(814)
Netting adjustment	2,315	4,979
Total net risk management derivatives - Liability	(118)	(99)
Mortgage commitments to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	4,370	4,143
Derivative asset, estimated fair value	29	9
Derivative Liabilities [Abstract]
Notional amount	57	1,570
Derivative liability, estimated fair value	0	(2)
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	40,650	45,925
Derivative asset, estimated fair value	349	108
Derivative Liabilities [Abstract]
Notional amount	1,045	21,099
Derivative liability, estimated fair value	(3)	(21)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	292	19,320
Derivative asset, estimated fair value	1	15
Derivative Liabilities [Abstract]
Notional amount	70,593	85,556
Derivative liability, estimated fair value	(645)	(205)
Mortgage commitment derivatives
Asset Derivatives [Abstract]
Notional amount	45,312	69,388
Derivative asset, estimated fair value	379	132
Netting adjustment	0	0
Derivative Liabilities [Abstract]
Notional amount	71,695	108,225
Derivative liability, estimated fair value	(648)	(228)
Netting adjustment	0	0
Credit enhancement derivatives
Asset Derivatives [Abstract]
Notional amount	33,431	13,240
Derivative asset, estimated fair value	57	22
Derivative Liabilities [Abstract]
Notional amount	919	0
Derivative liability, estimated fair value	$ (11)	$ (1)

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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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