Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Asset Derivatives [Abstract]
Notional amount	$ 224,699	$ 156,763
Derivative asset, estimated fair value	284	687
Netting adjustment	(4,034)	(4,514)
Liability Derivatives [Abstract]
Notional amount	310,179	339,456
Derivative liability, estimated fair value	(337)	(1,215)
Netting adjustment	4,877	6,844
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	1,500	2,900
Cash collateral received for derivative instruments	690	535
Risk Management Derivatives
Asset Derivatives [Abstract]
Notional amount	129,119	86,272
Derivative asset, estimated fair value	3,373	3,785
Accrued interest receivable (payable)	724	785
Netting adjustment	(4,034)	(4,514)
Total net risk management derivatives	63	56
Liability Derivatives [Abstract]
Notional amount	211,734	261,475
Derivative liability, estimated fair value	(4,097)	(6,385)
Accrued interest receivable (payable)	(907)	(937)
Netting adjustment	4,877	6,844
Total net risk management derivatives	(127)	(478)
Mortgage commitment derivatives
Asset Derivatives [Abstract]
Notional amount	95,580	70,491
Derivative asset, estimated fair value	221	631
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	98,445	77,981
Derivative liability, estimated fair value	(210)	(737)
Netting adjustment	0	0
Pay-fixed Swap
Asset Derivatives [Abstract]
Notional amount	40,400	29,540
Derivative asset, estimated fair value	472	660
Liability Derivatives [Abstract]
Notional amount	75,647	94,584
Derivative liability, estimated fair value	(2,639)	(4,396)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	46,989	30,207
Derivative asset, estimated fair value	2,554	2,696
Liability Derivatives [Abstract]
Notional amount	124,153	135,470
Derivative liability, estimated fair value	(1,109)	(1,552)
Basis Swap
Asset Derivatives [Abstract]
Notional amount	6,524	1,624
Derivative asset, estimated fair value	129	115
Liability Derivatives [Abstract]
Notional amount	600	15,600
Derivative liability, estimated fair value	0	(11)
Foreign Currency Swap
Asset Derivatives [Abstract]
Notional amount	232	214
Derivative asset, estimated fair value	54	40
Liability Derivatives [Abstract]
Notional amount	234	216
Derivative liability, estimated fair value	(64)	(85)
Pay-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	10,250	9,600
Derivative asset, estimated fair value	141	241
Liability Derivatives [Abstract]
Notional amount	2,750	4,850
Derivative liability, estimated fair value	(4)	(82)
Receive-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	400	0
Derivative asset, estimated fair value	0	0
Liability Derivatives [Abstract]
Notional amount	8,350	10,100
Derivative liability, estimated fair value	(280)	(257)
Other
Asset Derivatives [Abstract]
Notional amount	24,324	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	1,227	4,753
Derivative asset, estimated fair value	2	28
Liability Derivatives [Abstract]
Notional amount	6,808	3,039
Derivative liability, estimated fair value	(18)	(49)
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	16,572	31,635
Derivative asset, estimated fair value	38	198
Liability Derivatives [Abstract]
Notional amount	55,847	27,297
Derivative liability, estimated fair value	(137)	(388)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	77,781	34,103
Derivative asset, estimated fair value	181	405
Liability Derivatives [Abstract]
Notional amount	35,790	47,645
Derivative liability, estimated fair value	$ (55)	$ (300)