Derivative Instruments - Notional and Fair Value Position (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Derivative [Line Items]
Notional amount	$ 423,143	$ 366,384
Asset Derivatives
Derivative assets, gross amount offset	(109)	(237)
Derivative assets	1,824	171
Liability Derivatives
Derivatives liabilities at fair value	(1,204)	(233)
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	2,800	966
Cash collateral received for derivative instruments	45	30
Total risk management derivatives portfolio
Derivative [Line Items]
Notional amount	211,213	164,742
Asset Derivatives
Derivative assets, gross amount offset	(109)	(237)
Derivative assets	82	2
Liability Derivatives
Netting adjustment	2,881	1,173
Derivatives liabilities at fair value	(35)	(15)
Total risk management derivatives portfolio | Designated as Hedging Instrument
Derivative [Line Items]
Notional amount	49,791	45,033
Asset Derivatives
Derivative assets, gross	0	0
Liability Derivatives
Derivative liabilities, gross	(8)	0
Total risk management derivatives portfolio | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional amount	161,422	119,709
Asset Derivatives
Derivative assets, gross	191	239
Liability Derivatives
Derivative liabilities, gross	(2,908)	(1,188)
Pay-fixed Swap | Designated as Hedging Instrument
Derivative [Line Items]
Notional amount	5,527	4,347
Asset Derivatives
Derivative assets, gross	0	0
Liability Derivatives
Derivative liabilities, gross	0	0
Pay-fixed Swap | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional amount	67,940	56,817
Asset Derivatives
Derivative assets, gross	0	0
Liability Derivatives
Derivative liabilities, gross	0	0
Receive-fixed Swap | Designated as Hedging Instrument
Derivative [Line Items]
Notional amount	44,264	40,686
Asset Derivatives
Derivative assets, gross	0	0
Liability Derivatives
Derivative liabilities, gross	(8)	0
Receive-fixed Swap | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional amount	63,074	56,874
Asset Derivatives
Derivative assets, gross	0	0
Liability Derivatives
Derivative liabilities, gross	(2,850)	(1,131)
Basis Swap | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional amount	24,750	250
Asset Derivatives
Derivative assets, gross	82	152
Liability Derivatives
Derivative liabilities, gross	0	0
Foreign Currency Swap | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional amount	326	336
Asset Derivatives
Derivative assets, gross	7	25
Liability Derivatives
Derivative liabilities, gross	(37)	(34)
Pay-fixed Swaption | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional amount	4,241	4,341
Asset Derivatives
Derivative assets, gross	94	52
Liability Derivatives
Derivative liabilities, gross	0	(2)
Receive-fixed Swaption | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional amount	1,091	1,091
Asset Derivatives
Derivative assets, gross	8	10
Liability Derivatives
Derivative liabilities, gross	(21)	(21)
Mortgage commitment derivatives
Derivative [Line Items]
Notional amount	190,310	182,386
Asset Derivatives
Derivative assets, gross amount offset	0	0
Derivative assets	1,739	169
Liability Derivatives
Netting adjustment	0	0
Derivatives liabilities at fair value	(1,141)	(197)
Mortgage commitments to purchase whole loans
Derivative [Line Items]
Notional amount	12,107	13,192
Asset Derivatives
Derivative assets	23	17
Liability Derivatives
Derivatives liabilities at fair value	(96)	(5)
Forward contracts to purchase mortgage-related securities
Derivative [Line Items]
Notional amount	70,751	58,021
Asset Derivatives
Derivative assets	64	83
Liability Derivatives
Derivatives liabilities at fair value	(958)	(34)
Forward contracts to sell mortgage-related securities
Derivative [Line Items]
Notional amount	107,452	111,173
Asset Derivatives
Derivative assets	1,652	69
Liability Derivatives
Derivatives liabilities at fair value	(87)	(158)
Other
Derivative [Line Items]
Notional amount	21,620	19,256
Asset Derivatives
Derivative assets	3	0
Liability Derivatives
Derivatives liabilities at fair value	$ (28)	$ (21)