Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Asset Derivatives [Abstract]
Notional amount	$ 289,006	$ 266,935
Derivative asset, estimated fair value	584	458
Netting adjustment	(1,781)	(2,266)
Liability Derivatives [Abstract]
Notional amount	189,016	161,488
Derivative liability, estimated fair value	(793)	(777)
Netting adjustment	2,126	2,315
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	882	713
Cash collateral received for derivative instruments	537	664
Pay-fixed Swap
Asset Derivatives [Abstract]
Notional amount	70,599	71,416
Derivative asset, estimated fair value	171	438
Liability Derivatives [Abstract]
Notional amount	22,538	21,253
Derivative liability, estimated fair value	(823)	(740)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	89,157	88,799
Derivative asset, estimated fair value	1,037	1,113
Liability Derivatives [Abstract]
Notional amount	53,059	58,399
Derivative liability, estimated fair value	(541)	(860)
Basis Swap
Asset Derivatives [Abstract]
Notional amount	273	250
Derivative asset, estimated fair value	129	104
Liability Derivatives [Abstract]
Notional amount	0	624
Derivative liability, estimated fair value	0	0
Foreign Currency Swap
Asset Derivatives [Abstract]
Notional amount	226	221
Derivative asset, estimated fair value	35	22
Liability Derivatives [Abstract]
Notional amount	228	223
Derivative liability, estimated fair value	(66)	(72)
Pay-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	5,350	10,375
Derivative asset, estimated fair value	46	191
Liability Derivatives [Abstract]
Notional amount	5,625	1,000
Derivative liability, estimated fair value	(45)	(4)
Receive-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	1,100	500
Derivative asset, estimated fair value	51	20
Liability Derivatives [Abstract]
Notional amount	6,375	7,375
Derivative liability, estimated fair value	(287)	(338)
Future [Member]
Asset Derivatives [Abstract]
Notional amount	21,594	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	188,299	188,192
Derivative asset, estimated fair value	1,469	1,888
Accrued interest receivable (payable)	395	400
Netting adjustment	(1,781)	(2,266)
Total net risk management derivatives	83	22
Liability Derivatives [Abstract]
Notional amount	87,825	88,874
Derivative liability, estimated fair value	(1,762)	(2,014)
Accrued interest receivable (payable)	(462)	(419)
Netting adjustment	2,126	2,315
Total net risk management derivatives	(98)	(118)
Mortgage commitments to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	3,901	4,370
Derivative asset, estimated fair value	26	29
Liability Derivatives [Abstract]
Notional amount	2,153	57
Derivative liability, estimated fair value	(3)	0
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	53,514	40,650
Derivative asset, estimated fair value	403	349
Liability Derivatives [Abstract]
Notional amount	9,649	1,045
Derivative liability, estimated fair value	(10)	(3)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	10,547	292
Derivative asset, estimated fair value	10	1
Liability Derivatives [Abstract]
Notional amount	86,515	70,593
Derivative liability, estimated fair value	(653)	(645)
Mortgage commitment derivatives
Asset Derivatives [Abstract]
Notional amount	67,962	45,312
Derivative asset, estimated fair value	439	379
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	98,317	71,695
Derivative liability, estimated fair value	(666)	(648)
Netting adjustment	0	0
Other
Asset Derivatives [Abstract]
Notional amount	32,745	33,431
Derivative asset, estimated fair value	62	57
Liability Derivatives [Abstract]
Notional amount	2,874	919
Derivative liability, estimated fair value	$ (29)	$ (11)