Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Asset Derivatives [Abstract]
Notional amount	$ 307,347	$ 266,935
Derivative asset, estimated fair value	561	458
Netting adjustment	(1,709)	(2,266)
Liability Derivatives [Abstract]
Notional amount	238,750	161,488
Derivative liability, estimated fair value	(799)	(777)
Netting adjustment	2,297	2,315
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	1,200	713
Cash collateral received for derivative instruments	573	664
Pay-fixed Swap
Asset Derivatives [Abstract]
Notional amount	58,357	71,416
Derivative asset, estimated fair value	4	438
Liability Derivatives [Abstract]
Notional amount	31,468	21,253
Derivative liability, estimated fair value	(1,327)	(740)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	91,919	88,799
Derivative asset, estimated fair value	1,096	1,113
Liability Derivatives [Abstract]
Notional amount	47,254	58,399
Derivative liability, estimated fair value	(210)	(860)
Basis Swap
Asset Derivatives [Abstract]
Notional amount	273	250
Derivative asset, estimated fair value	155	104
Liability Derivatives [Abstract]
Notional amount	0	624
Derivative liability, estimated fair value	0	0
Foreign Currency Swap
Asset Derivatives [Abstract]
Notional amount	220	221
Derivative asset, estimated fair value	30	22
Liability Derivatives [Abstract]
Notional amount	222	223
Derivative liability, estimated fair value	(77)	(72)
Pay-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	4,600	10,375
Derivative asset, estimated fair value	29	191
Liability Derivatives [Abstract]
Notional amount	6,375	1,000
Derivative liability, estimated fair value	(172)	(4)
Receive-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	2,125	500
Derivative asset, estimated fair value	90	20
Liability Derivatives [Abstract]
Notional amount	5,350	7,375
Derivative liability, estimated fair value	(232)	(338)
Future [Member]
Asset Derivatives [Abstract]
Notional amount	19,537	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	177,031	188,192
Derivative asset, estimated fair value	1,404	1,888
Accrued interest receivable (payable)	360	400
Netting adjustment	(1,709)	(2,266)
Total net risk management derivatives	55	22
Liability Derivatives [Abstract]
Notional amount	90,669	88,874
Derivative liability, estimated fair value	(2,018)	(2,014)
Accrued interest receivable (payable)	(359)	(419)
Netting adjustment	2,297	2,315
Total net risk management derivatives	(80)	(118)
Mortgage commitments to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	9,767	4,370
Derivative asset, estimated fair value	54	29
Liability Derivatives [Abstract]
Notional amount	2,417	57
Derivative liability, estimated fair value	(2)	0
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	78,510	40,650
Derivative asset, estimated fair value	389	349
Liability Derivatives [Abstract]
Notional amount	10,000	1,045
Derivative liability, estimated fair value	(11)	(3)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	10,230	292
Derivative asset, estimated fair value	12	1
Liability Derivatives [Abstract]
Notional amount	131,017	70,593
Derivative liability, estimated fair value	(675)	(645)
Mortgage commitment derivatives
Asset Derivatives [Abstract]
Notional amount	98,507	45,312
Derivative asset, estimated fair value	455	379
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	143,434	71,695
Derivative liability, estimated fair value	(688)	(648)
Netting adjustment	0	0
Other
Asset Derivatives [Abstract]
Notional amount	31,809	33,431
Derivative asset, estimated fair value	51	57
Liability Derivatives [Abstract]
Notional amount	4,647	919
Derivative liability, estimated fair value	$ (31)	$ (11)