Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Asset Derivatives [Abstract]
Notional amount	$ 228,247	$ 156,763
Derivative asset, estimated fair value	419	687
Netting adjustment	(4,024)	(4,514)
Liability Derivatives [Abstract]
Notional amount	319,162	339,456
Derivative liability, estimated fair value	(420)	(1,215)
Netting adjustment	5,034	6,844
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	1,600	2,900
Cash collateral received for derivative instruments	599	535
Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	114,188	86,272
Derivative asset, estimated fair value	3,423	3,785
Accrued interest receivable	707	785
Netting adjustment	(4,024)	(4,514)
Total net risk management derivatives	106	56
Liability Derivatives [Abstract]
Notional amount	226,328	261,475
Derivative liability, estimated fair value	(4,382)	(6,385)
Accrued interest payable	(754)	(937)
Netting adjustment	5,034	6,844
Total net risk management derivatives	(102)	(478)
Mortgage commitment derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	114,059	70,491
Derivative asset, estimated fair value	313	631
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	92,834	77,981
Derivative liability, estimated fair value	(318)	(737)
Netting adjustment	0	0
Pay-fixed Swap
Asset Derivatives [Abstract]
Notional amount	32,746	29,540
Derivative asset, estimated fair value	441	660
Liability Derivatives [Abstract]
Notional amount	79,878	94,584
Derivative liability, estimated fair value	(2,983)	(4,396)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	33,890	30,207
Derivative asset, estimated fair value	2,604	2,696
Liability Derivatives [Abstract]
Notional amount	134,172	135,470
Derivative liability, estimated fair value	(1,051)	(1,552)
Basis Swap
Asset Derivatives [Abstract]
Notional amount	12,873	1,624
Derivative asset, estimated fair value	127	115
Liability Derivatives [Abstract]
Notional amount	1,350	15,600
Derivative liability, estimated fair value	(1)	(11)
Foreign Currency Swap
Asset Derivatives [Abstract]
Notional amount	226	214
Derivative asset, estimated fair value	49	40
Liability Derivatives [Abstract]
Notional amount	228	216
Derivative liability, estimated fair value	(72)	(85)
Pay-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	10,250	9,600
Derivative asset, estimated fair value	179	241
Liability Derivatives [Abstract]
Notional amount	2,350	4,850
Derivative liability, estimated fair value	(3)	(82)
Receive-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	0	0
Derivative asset, estimated fair value	0	0
Liability Derivatives [Abstract]
Notional amount	8,350	10,100
Derivative liability, estimated fair value	(271)	(257)
Other
Asset Derivatives [Abstract]
Notional amount	24,203	15,087
Derivative asset, estimated fair value	23	33
Liability Derivatives [Abstract]
Notional amount	0	655
Derivative liability, estimated fair value	(1)	(2)
Mortgage commitments to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	1,898	4,753
Derivative asset, estimated fair value	5	28
Liability Derivatives [Abstract]
Notional amount	6,698	3,039
Derivative liability, estimated fair value	(27)	(49)
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	11,791	31,635
Derivative asset, estimated fair value	37	198
Liability Derivatives [Abstract]
Notional amount	69,343	27,297
Derivative liability, estimated fair value	(243)	(388)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	100,370	34,103
Derivative asset, estimated fair value	271	405
Liability Derivatives [Abstract]
Notional amount	16,793	47,645
Derivative liability, estimated fair value	$ (48)	$ (300)