Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Asset Derivatives [Abstract]
Notional amount	$ 220,861	$ 175,667
Derivative asset, estimated fair value	490	894
Netting adjustment	(6,154)	(4,024)
Liability Derivatives [Abstract]
Notional amount	368,074	375,704
Derivative liability, estimated fair value	(702)	(424)
Netting adjustment	12,423	8,650
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	6,700	4,900
Cash collateral received for derivative instruments	419	314
Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	124,738	113,355
Derivative asset, estimated fair value	5,575	4,020
Accrued interest receivable	720	758
Netting adjustment	(6,154)	(4,024)
Total net risk management derivatives - Asset	141	754
Liability Derivatives [Abstract]
Notional amount	227,787	312,573
Derivative liability, estimated fair value	(11,491)	(7,939)
Accrued interest payable	(1,097)	(977)
Netting adjustment	12,423	8,650
Total net risk management derivatives - Liability	(165)	(266)
Mortgage commitment derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	96,123	62,312
Derivative asset, estimated fair value	349	140
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	140,287	63,131
Derivative liability, estimated fair value	(537)	(158)
Netting adjustment	0	0
Pay-fixed Swap
Asset Derivatives [Abstract]
Notional amount	6,324	33,154
Derivative asset, estimated fair value	19	267
Liability Derivatives [Abstract]
Notional amount	127,859	123,106
Derivative liability, estimated fair value	(11,071)	(6,920)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	99,254	59,796
Derivative asset, estimated fair value	5,218	3,436
Liability Derivatives [Abstract]
Notional amount	70,551	143,209
Derivative liability, estimated fair value	(146)	(753)
Basis Swap
Asset Derivatives [Abstract]
Notional amount	1,764	1,864
Derivative asset, estimated fair value	198	141
Liability Derivatives [Abstract]
Notional amount	15,700	17,100
Derivative liability, estimated fair value	(21)	(15)
Foreign Currency Swap
Asset Derivatives [Abstract]
Notional amount	225	295
Derivative asset, estimated fair value	75	95
Liability Derivatives [Abstract]
Notional amount	227	258
Derivative liability, estimated fair value	(82)	(52)
Pay-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	6,175	7,050
Derivative asset, estimated fair value	36	45
Liability Derivatives [Abstract]
Notional amount	6,850	14,950
Derivative liability, estimated fair value	(13)	(26)
Received-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	1,625	2,000
Derivative asset, estimated fair value	7	8
Liability Derivatives [Abstract]
Notional amount	6,600	13,950
Derivative liability, estimated fair value	(157)	(171)
Other [Member]
Asset Derivatives [Abstract]
Notional amount	9,371	9,196
Derivative asset, estimated fair value	22	28
Liability Derivatives [Abstract]
Notional amount	0	0
Derivative liability, estimated fair value	(1)	(2)
Mortgage commitment to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	10,820	4,815
Derivative asset, estimated fair value	31	9
Liability Derivatives [Abstract]
Notional amount	4,568	2,960
Derivative liability, estimated fair value	(6)	(9)
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	66,637	31,273
Derivative asset, estimated fair value	280	66
Liability Derivatives [Abstract]
Notional amount	18,467	19,418
Derivative liability, estimated fair value	(29)	(57)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	18,666	26,224
Derivative asset, estimated fair value	38	65
Liability Derivatives [Abstract]
Notional amount	117,252	40,753
Derivative liability, estimated fair value	$ (502)	$ (92)