Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Asset Derivatives [Abstract]
Notional amount	$ 178,138	$ 156,763
Derivative asset, estimated fair value	171	687
Netting adjustment	(4,272)	(4,514)
Derivative Liabilities [Abstract]
Notional amount	338,089	339,456
Derivative liability, estimated fair value	(328)	(1,215)
Netting adjustment	4,979	6,844
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	1,400	2,900
Cash collateral received for derivative instruments	649	535
Pay-fixed swap
Asset Derivatives [Abstract]
Notional amount	52,732	29,540
Derivative asset, estimated fair value	772	660
Derivative Liabilities [Abstract]
Notional amount	70,211	94,584
Derivative liability, estimated fair value	(2,120)	(4,396)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	31,671	30,207
Derivative asset, estimated fair value	2,391	2,696
Derivative Liabilities [Abstract]
Notional amount	138,852	135,470
Derivative liability, estimated fair value	(1,764)	(1,552)
Basis swap
Asset Derivatives [Abstract]
Notional amount	873	1,624
Derivative asset, estimated fair value	124	115
Derivative Liabilities [Abstract]
Notional amount	0	15,600
Derivative liability, estimated fair value	0	(11)
Foreign currency swap
Asset Derivatives [Abstract]
Notional amount	234	214
Derivative asset, estimated fair value	59	40
Derivative Liabilities [Abstract]
Notional amount	236	216
Derivative liability, estimated fair value	(56)	(85)
Pay-fixed swaption
Asset Derivatives [Abstract]
Notional amount	9,750	9,600
Derivative asset, estimated fair value	95	241
Derivative Liabilities [Abstract]
Notional amount	4,000	4,850
Derivative liability, estimated fair value	(20)	(82)
Receive-fixed swaption
Asset Derivatives [Abstract]
Notional amount	250	0
Derivative asset, estimated fair value	13	0
Derivative Liabilities [Abstract]
Notional amount	9,250	10,100
Derivative liability, estimated fair value	(304)	(257)
Other
Asset Derivatives [Abstract]
Notional amount	13,240	15,087
Derivative asset, estimated fair value	22	33
Derivative Liabilities [Abstract]
Notional amount	7,315	655
Derivative liability, estimated fair value	(1)	(2)
Risk management derivatives
Asset Derivatives [Abstract]
Notional amount	108,750	86,272
Derivative asset, estimated fair value	3,476	3,785
Accrued interest receivable	835	785
Netting adjustment	(4,272)	(4,514)
Total net risk management derivatives - Asset	39	56
Derivative Liabilities [Abstract]
Notional amount	229,864	261,475
Derivative liability, estimated fair value	(4,265)	(6,385)
Accrued interest payable	(814)	(937)
Netting adjustment	4,979	6,844
Total net risk management derivatives - Liability	(100)	(478)
Mortgage commitments to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	4,143	4,753
Derivative asset, estimated fair value	9	28
Derivative Liabilities [Abstract]
Notional amount	1,570	3,039
Derivative liability, estimated fair value	(2)	(49)
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	45,925	31,635
Derivative asset, estimated fair value	108	198
Derivative Liabilities [Abstract]
Notional amount	21,099	27,297
Derivative liability, estimated fair value	(21)	(388)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	19,320	34,103
Derivative asset, estimated fair value	15	405
Derivative Liabilities [Abstract]
Notional amount	85,556	47,645
Derivative liability, estimated fair value	(205)	(300)
Mortgage commitment derivatives
Asset Derivatives [Abstract]
Notional amount	69,388	70,491
Derivative asset, estimated fair value	132	631
Netting adjustment	0	0
Derivative Liabilities [Abstract]
Notional amount	108,225	77,981
Derivative liability, estimated fair value	(228)	(737)
Netting adjustment	$ 0	$ 0