Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Asset Derivatives [Abstract]
Notional amount	$ 327,339	$ 266,935
Derivative asset, estimated fair value	472	458
Netting adjustment	(1,663)	(2,266)
Liability Derivatives [Abstract]
Notional amount	229,918	161,488
Derivative liability, estimated fair value	(595)	(777)
Netting adjustment	2,299	2,315
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	1,300	713
Cash collateral received for derivative instruments	684	664
Pay-fixed Swap
Asset Derivatives [Abstract]
Notional amount	35,550	71,416
Derivative asset, estimated fair value	0	438
Liability Derivatives [Abstract]
Notional amount	32,893	21,253
Derivative liability, estimated fair value	(1,481)	(740)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	71,372	88,799
Derivative asset, estimated fair value	958	1,113
Liability Derivatives [Abstract]
Notional amount	34,986	58,399
Derivative liability, estimated fair value	(103)	(860)
Basis Swap
Asset Derivatives [Abstract]
Notional amount	273	250
Derivative asset, estimated fair value	179	104
Liability Derivatives [Abstract]
Notional amount	0	624
Derivative liability, estimated fair value	0	0
Foreign Currency Swap
Asset Derivatives [Abstract]
Notional amount	213	221
Derivative asset, estimated fair value	27	22
Liability Derivatives [Abstract]
Notional amount	215	223
Derivative liability, estimated fair value	(86)	(72)
Pay-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	4,600	10,375
Derivative asset, estimated fair value	18	191
Liability Derivatives [Abstract]
Notional amount	6,375	1,000
Derivative liability, estimated fair value	(270)	(4)
Receive-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	2,875	500
Derivative asset, estimated fair value	203	20
Liability Derivatives [Abstract]
Notional amount	4,600	7,375
Derivative liability, estimated fair value	(137)	(338)
Future [Member]
Asset Derivatives [Abstract]
Notional amount	47,069	16,631
Derivative asset, estimated fair value	0	0
Liability Derivatives [Abstract]
Notional amount	0	0
Derivative liability, estimated fair value	0	0
Risk Management Derivatives
Asset Derivatives [Abstract]
Notional amount	161,952	188,192
Derivative asset, estimated fair value	1,385	1,888
Accrued interest receivable (payable)	287	400
Netting adjustment	(1,663)	(2,266)
Total net risk management derivatives	9	22
Liability Derivatives [Abstract]
Notional amount	79,069	88,874
Derivative liability, estimated fair value	(2,077)	(2,014)
Accrued interest receivable (payable)	(374)	(419)
Netting adjustment	2,299	2,315
Total net risk management derivatives	(152)	(118)
Mortgage commitments to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	7,812	4,370
Derivative asset, estimated fair value	20	29
Liability Derivatives [Abstract]
Notional amount	6,258	57
Derivative liability, estimated fair value	(26)	0
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	70,120	40,650
Derivative asset, estimated fair value	231	349
Liability Derivatives [Abstract]
Notional amount	28,853	1,045
Derivative liability, estimated fair value	(85)	(3)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	57,048	292
Derivative asset, estimated fair value	170	1
Liability Derivatives [Abstract]
Notional amount	109,229	70,593
Derivative liability, estimated fair value	(305)	(645)
Mortgage commitment derivatives
Asset Derivatives [Abstract]
Notional amount	134,980	45,312
Derivative asset, estimated fair value	421	379
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	144,340	71,695
Derivative liability, estimated fair value	(416)	(648)
Netting adjustment	0	0
Other
Asset Derivatives [Abstract]
Notional amount	30,407	33,431
Derivative asset, estimated fair value	42	57
Liability Derivatives [Abstract]
Notional amount	6,509	919
Derivative liability, estimated fair value	$ (27)	$ (11)