Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Asset Derivatives [Abstract]
Notional amount	$ 441,661	$ 243,475
Derivative asset, estimated fair value	904	271
Netting adjustment	(2,108)	(1,288)
Liability Derivatives [Abstract]
Notional amount	277,818	196,666
Derivative liability, estimated fair value	(1,380)	(435)
Netting adjustment	2,396	1,694
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	1,200	1,000
Cash collateral received for derivative instruments	906	635
Pay-fixed Swap
Asset Derivatives [Abstract]
Notional amount	98,953	41,052
Derivative asset, estimated fair value	0	0
Liability Derivatives [Abstract]
Notional amount	28,553	29,178
Derivative liability, estimated fair value	(1,747)	(970)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	131,314	73,579
Derivative asset, estimated fair value	1,143	816
Liability Derivatives [Abstract]
Notional amount	4,851	26,382
Derivative liability, estimated fair value	(3)	(62)
Basis Swap
Asset Derivatives [Abstract]
Notional amount	250	273
Derivative asset, estimated fair value	222	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	32	39
Liability Derivatives [Abstract]
Notional amount	217	232
Derivative liability, estimated fair value	(91)	(65)
Pay-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	4,600	4,600
Derivative asset, estimated fair value	6	18
Liability Derivatives [Abstract]
Notional amount	5,875	6,375
Derivative liability, estimated fair value	(340)	(219)
Receive-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	6,625	2,875
Derivative asset, estimated fair value	648	106
Liability Derivatives [Abstract]
Notional amount	350	4,600
Derivative liability, estimated fair value	(134)	(232)
Future [Member]
Asset Derivatives [Abstract]
Notional amount	15,982	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	257,939	143,115
Derivative asset, estimated fair value	2,051	1,128
Accrued interest receivable (payable)	109	226
Netting adjustment	(2,108)	(1,288)
Total net risk management derivatives	52	66
Liability Derivatives [Abstract]
Notional amount	39,846	66,767
Derivative liability, estimated fair value	(2,315)	(1,548)
Accrued interest receivable (payable)	(193)	(250)
Netting adjustment	2,396	1,694
Total net risk management derivatives	(112)	(104)
Mortgage commitments to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	41,032	7,115
Derivative asset, estimated fair value	175	15
Liability Derivatives [Abstract]
Notional amount	1,141	1,787
Derivative liability, estimated fair value	(1)	(1)
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	106,225	55,531
Derivative asset, estimated fair value	571	137
Liability Derivatives [Abstract]
Notional amount	13,080	9,560
Derivative liability, estimated fair value	(21)	(28)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	12,131	9,282
Derivative asset, estimated fair value	21	13
Liability Derivatives [Abstract]
Notional amount	212,592	109,066
Derivative liability, estimated fair value	(1,202)	(277)
Mortgage commitment derivatives
Asset Derivatives [Abstract]
Notional amount	159,388	71,928
Derivative asset, estimated fair value	767	165
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	226,813	120,413
Derivative liability, estimated fair value	(1,224)	(306)
Netting adjustment	0	0
Other
Asset Derivatives [Abstract]
Notional amount	24,334	28,432
Derivative asset, estimated fair value	85	40
Liability Derivatives [Abstract]
Notional amount	11,159	9,486
Derivative liability, estimated fair value	$ (44)	$ (25)