Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Asset Derivatives [Abstract]
Notional amount	$ 305,424	$ 178,138
Derivative asset, estimated fair value	315	171
Netting adjustment	(2,744)	(4,272)
Liability Derivatives [Abstract]
Notional amount	216,034	338,089
Derivative liability, estimated fair value	(663)	(328)
Netting adjustment	2,867	4,979
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	755	1,400
Cash collateral received for derivative instruments	633	649
Risk Management Derivatives
Asset Derivatives [Abstract]
Notional amount	230,927	108,750
Derivative asset, estimated fair value	2,404	3,476
Accrued interest receivable (payable)	378	835
Netting adjustment	(2,744)	(4,272)
Total net risk management derivatives	38	39
Liability Derivatives [Abstract]
Notional amount	98,787	229,864
Derivative liability, estimated fair value	(2,499)	(4,265)
Accrued interest receivable (payable)	(521)	(814)
Netting adjustment	2,867	4,979
Total net risk management derivatives	(153)	(100)
Mortgage commitment derivatives
Asset Derivatives [Abstract]
Notional amount	74,497	69,388
Derivative asset, estimated fair value	277	132
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	117,247	108,225
Derivative liability, estimated fair value	(510)	(228)
Netting adjustment	0	0
Pay-fixed Swap
Asset Derivatives [Abstract]
Notional amount	92,573	52,732
Derivative asset, estimated fair value	601	772
Liability Derivatives [Abstract]
Notional amount	24,643	70,211
Derivative liability, estimated fair value	(878)	(2,120)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	105,051	31,671
Derivative asset, estimated fair value	1,371	2,391
Liability Derivatives [Abstract]
Notional amount	61,174	138,852
Derivative liability, estimated fair value	(1,254)	(1,764)
Basis Swap
Asset Derivatives [Abstract]
Notional amount	273	873
Derivative asset, estimated fair value	102	124
Liability Derivatives [Abstract]
Notional amount	600	0
Derivative liability, estimated fair value	(1)	0
Foreign Currency Swap
Asset Derivatives [Abstract]
Notional amount	243	234
Derivative asset, estimated fair value	62	59
Liability Derivatives [Abstract]
Notional amount	245	236
Derivative liability, estimated fair value	(43)	(56)
Pay-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	11,375	9,750
Derivative asset, estimated fair value	222	95
Liability Derivatives [Abstract]
Notional amount	2,750	4,000
Derivative liability, estimated fair value	(5)	(20)
Receive-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	500	250
Derivative asset, estimated fair value	21	13
Liability Derivatives [Abstract]
Notional amount	9,375	9,250
Derivative liability, estimated fair value	(317)	(304)
Other
Asset Derivatives [Abstract]
Notional amount	20,912	13,240
Derivative asset, estimated fair value	25	22
Liability Derivatives [Abstract]
Notional amount	0	7,315
Derivative liability, estimated fair value	(1)	(1)
Mortgage commitments to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	5,490	4,143
Derivative asset, estimated fair value	18	9
Liability Derivatives [Abstract]
Notional amount	575	1,570
Derivative liability, estimated fair value	(2)	(2)
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	63,336	45,925
Derivative asset, estimated fair value	227	108
Liability Derivatives [Abstract]
Notional amount	8,092	21,099
Derivative liability, estimated fair value	(40)	(21)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	5,671	19,320
Derivative asset, estimated fair value	32	15
Liability Derivatives [Abstract]
Notional amount	108,580	85,556
Derivative liability, estimated fair value	$ (468)	$ (205)