Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Asset Derivatives [Abstract]
Notional amount	$ 435,855	$ 450,981
Derivative asset, estimated fair value	2,672	1,225
Netting adjustment	(655)	(905)
Liability Derivatives [Abstract]
Notional amount	267,695	288,198
Derivative liability, estimated fair value	(2,106)	(1,495)
Netting adjustment	1,632	995
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	1,000	658
Cash collateral received for derivative instruments	35	568
Pay-fixed Swap
Asset Derivatives [Abstract]
Notional amount	68,674	88,361
Derivative asset, estimated fair value	0	0
Liability Derivatives [Abstract]
Notional amount	9,636	11,461
Derivative liability, estimated fair value	(482)	(595)
Pay-fixed Swap | Fair Value Hedging | Designated as Hedging Instrument
Asset Derivatives [Abstract]
Notional amount	2,804	0
Derivative asset, estimated fair value	0	0
Liability Derivatives [Abstract]
Notional amount	75	0
Derivative liability, estimated fair value	(7)	0
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	45,635	92,315
Derivative asset, estimated fair value	167	233
Liability Derivatives [Abstract]
Notional amount	46,039	33,919
Derivative liability, estimated fair value	(1,035)	(123)
Receive-fixed Swap | Fair Value Hedging | Designated as Hedging Instrument
Asset Derivatives [Abstract]
Notional amount	39,754	0
Derivative asset, estimated fair value	2	0
Liability Derivatives [Abstract]
Notional amount	0	0
Derivative liability, estimated fair value	0	0
Basis Swap
Asset Derivatives [Abstract]
Notional amount	250	250
Derivative asset, estimated fair value	146	192
Liability Derivatives [Abstract]
Notional amount	0	0
Derivative liability, estimated fair value	0	0
Foreign Currency Swap
Asset Derivatives [Abstract]
Notional amount	238	237
Derivative asset, estimated fair value	43	57
Liability Derivatives [Abstract]
Notional amount	241	239
Derivative liability, estimated fair value	(52)	(58)
Pay-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	5,690	5,530
Derivative asset, estimated fair value	124	37
Liability Derivatives [Abstract]
Notional amount	375	2,025
Derivative liability, estimated fair value	(16)	(118)
Receive-fixed Swaption
Asset Derivatives [Abstract]
Notional amount	1,455	3,355
Derivative asset, estimated fair value	96	346
Liability Derivatives [Abstract]
Notional amount	1,110	700
Derivative liability, estimated fair value	(42)	(16)
Future [Member]
Asset Derivatives [Abstract]
Notional amount	1,602	64,398
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	123,544	254,446
Derivative asset, estimated fair value	576	865
Accrued interest receivable (payable)	91	97
Netting adjustment	(655)	(905)
Liability Derivatives [Abstract]
Notional amount	57,401	48,344
Derivative liability, estimated fair value	(1,627)	(910)
Accrued interest (receivable) payable	(86)	(105)
Netting adjustment	1,632	995
Risk Management Derivatives | Not Designated as Hedging Instrument, Economic Hedge
Asset Derivatives [Abstract]
Notional amount	123,544	254,446
Total net risk management derivatives	667	962
Liability Derivatives [Abstract]
Notional amount	57,401	48,344
Total net risk management derivatives	(1,713)	(1,015)
Risk Management Derivatives | Fair Value Hedging | Designated as Hedging Instrument
Asset Derivatives [Abstract]
Accrued interest receivable (payable)	1	0
Liability Derivatives [Abstract]
Accrued interest (receivable) payable	0	0
Mortgage commitments to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	9,456	35,292
Derivative asset, estimated fair value	5	145
Liability Derivatives [Abstract]
Notional amount	22,709	51
Derivative liability, estimated fair value	(237)	0
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	26,155	144,215
Derivative asset, estimated fair value	57	844
Liability Derivatives [Abstract]
Notional amount	145,335	607
Derivative liability, estimated fair value	(1,689)	0
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	220,063	199
Derivative asset, estimated fair value	2,534	0
Liability Derivatives [Abstract]
Notional amount	31,765	227,828
Derivative liability, estimated fair value	(46)	(1,426)
Mortgage commitment derivatives
Asset Derivatives [Abstract]
Notional amount	255,674	179,706
Derivative asset, estimated fair value	2,596	989
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	199,809	228,486
Derivative liability, estimated fair value	(1,972)	(1,426)
Netting adjustment	0	0
Other
Asset Derivatives [Abstract]
Notional amount	14,079	16,829
Derivative asset, estimated fair value	61	179
Liability Derivatives [Abstract]
Notional amount	10,410	11,368
Derivative liability, estimated fair value	(46)	(49)
Fair Value Hedging | Designated as Hedging Instrument
Asset Derivatives [Abstract]
Notional amount	42,558	0
Derivative asset, estimated fair value	3	0
Liability Derivatives [Abstract]
Notional amount	75	0
Derivative liability, estimated fair value	(7)	0
Total risk management derivatives portfolio
Asset Derivatives [Abstract]
Notional amount	166,102	254,446
Total net risk management derivatives	15	57
Liability Derivatives [Abstract]
Notional amount	57,476	48,344
Total net risk management derivatives	$ (88)	$ (20)