Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Asset Derivatives [Abstract]
Notional amount	$ 180,655	$ 156,763
Derivative asset, estimated fair value	599	687
Netting adjustment	(4,104)	(4,514)
Liability Derivatives [Abstract]
Notional amount	349,778	339,456
Derivative liability, estimated fair value	(903)	(1,215)
Netting adjustment	5,397	6,844
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	1,900	2,900
Cash collateral received for derivative instruments	632	535
Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	100,319	86,272
Derivative asset, estimated fair value	3,643	3,785
Accrued interest receivable	643	785
Netting adjustment	(4,104)	(4,514)
Total net risk management derivatives	182	56
Liability Derivatives [Abstract]
Notional amount	242,751	261,475
Derivative liability, estimated fair value	(4,799)	(6,385)
Accrued interest payable	(918)	(937)
Netting adjustment	5,397	6,844
Total net risk management derivatives	(320)	(478)
Mortgage commitment derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	80,336	70,491
Derivative asset, estimated fair value	417	631
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	107,027	77,981
Derivative liability, estimated fair value	(583)	(737)
Netting adjustment	0	0
Pay-fixed Swap
Asset Derivatives [Abstract]
Notional amount	41,303	29,540
Derivative asset, estimated fair value	733	660
Liability Derivatives [Abstract]
Notional amount	78,857	94,584
Derivative liability, estimated fair value	(2,885)	(4,396)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	32,880	30,207
Derivative asset, estimated fair value	2,495	2,696
Liability Derivatives [Abstract]
Notional amount	140,428	135,470
Derivative liability, estimated fair value	(1,563)	(1,552)
Basis Swap
Asset Derivatives [Abstract]
Notional amount	1,623	1,624
Derivative asset, estimated fair value	113	115
Liability Derivatives [Abstract]
Notional amount	12,600	15,600
Derivative liability, estimated fair value	(2)	(11)
Foreign Currency Swap
Asset Derivatives [Abstract]
Notional amount	217	214
Derivative asset, estimated fair value	45	40
Liability Derivatives [Abstract]
Notional amount	220	216
Derivative liability, estimated fair value	(78)	(85)
Pay-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	9,600	9,600
Derivative asset, estimated fair value	230	241
Liability Derivatives [Abstract]
Notional amount	2,350	4,850
Derivative liability, estimated fair value	(7)	(82)
Receive-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	0	0
Derivative asset, estimated fair value	0	0
Liability Derivatives [Abstract]
Notional amount	7,600	10,100
Derivative liability, estimated fair value	(263)	(257)
Other [Member]
Asset Derivatives [Abstract]
Notional amount	14,696	15,087
Derivative asset, estimated fair value	27	33
Liability Derivatives [Abstract]
Notional amount	696	655
Derivative liability, estimated fair value	(1)	(2)
Mortgage commitments to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	6,931	4,753
Derivative asset, estimated fair value	26	28
Liability Derivatives [Abstract]
Notional amount	873	3,039
Derivative liability, estimated fair value	(1)	(49)
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	65,070	31,635
Derivative asset, estimated fair value	379	198
Liability Derivatives [Abstract]
Notional amount	7,373	27,297
Derivative liability, estimated fair value	(10)	(388)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	8,335	34,103
Derivative asset, estimated fair value	12	405
Liability Derivatives [Abstract]
Notional amount	98,781	47,645
Derivative liability, estimated fair value	$ (572)	$ (300)