Derivative Instruments - Notional and Fair Value Position (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Derivative [Line Items]
Notional Amount	$ 789,498	$ 668,079
Asset Derivatives
Derivative assets, gross amount offset	(206)	(199)
Derivative assets	499	177
Liability Derivatives
Derivatives liabilities at fair value	(640)	(152)
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	2,400	1,100
Cash collateral received for derivative instruments	(2)	(27)
Total risk management derivatives portfolio
Derivative [Line Items]
Notional Amount	520,275	477,083
Asset Derivatives
Derivative assets, gross amount offset	(206)	(199)
Derivative assets	210	78
Liability Derivatives
Netting adjustment	2,641	1,242
Derivatives liabilities at fair value	(24)	(14)
Total risk management derivatives portfolio | Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	57,551	47,198
Asset Derivatives
Derivative assets, gross	0	0
Liability Derivatives
Derivative liabilities, gross	0	0
Total risk management derivatives portfolio | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	462,724	429,885
Asset Derivatives
Derivative assets, gross	416	277
Liability Derivatives
Derivative liabilities, gross	(2,665)	(1,256)
Pay-fixed | Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	50,365	38,759
Asset Derivatives
Derivative assets, gross	0	0
Liability Derivatives
Derivative liabilities, gross	0	0
Pay-fixed | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	167,634	199,744
Asset Derivatives
Derivative assets, gross	0	0
Liability Derivatives
Derivative liabilities, gross	0	0
Receive-fixed | Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	7,186	8,439
Asset Derivatives
Derivative assets, gross	0	0
Liability Derivatives
Derivative liabilities, gross	0	0
Receive-fixed | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	220,497	194,394
Asset Derivatives
Derivative assets, gross	42	145
Liability Derivatives
Derivative liabilities, gross	(2,233)	(1,082)
Basis | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	250	250
Asset Derivatives
Derivative assets, gross	0	28
Liability Derivatives
Derivative liabilities, gross	(1)	0
Foreign currency | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	329	334
Asset Derivatives
Derivative assets, gross	0	0
Liability Derivatives
Derivative liabilities, gross	(63)	(56)
Pay-fixed | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	33,209	11,956
Asset Derivatives
Derivative assets, gross	319	91
Liability Derivatives
Derivative liabilities, gross	(190)	(4)
Receive-fixed | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	17,821	11,661
Asset Derivatives
Derivative assets, gross	11	13
Liability Derivatives
Derivative liabilities, gross	(169)	(114)
Futures | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	18,984	11,546
Asset Derivatives
Derivative assets, gross	0	0
Liability Derivatives
Derivative liabilities, gross	0	0
Interest rate caps | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	4,000	0
Asset Derivatives
Derivative assets, gross	44	0
Liability Derivatives
Derivative liabilities, gross	(9)	0
Mortgage commitment derivatives
Derivative [Line Items]
Notional Amount	239,760	162,995
Asset Derivatives
Derivative assets, gross amount offset	0	0
Derivative assets	241	55
Liability Derivatives
Netting adjustment	0	0
Derivatives liabilities at fair value	(529)	(131)
Mortgage commitments to purchase whole loans
Derivative [Line Items]
Notional Amount	4,260	4,005
Asset Derivatives
Derivative assets	0	7
Liability Derivatives
Derivatives liabilities at fair value	(42)	(1)
Forward contracts to purchase mortgage-related securities
Derivative [Line Items]
Notional Amount	92,692	47,122
Asset Derivatives
Derivative assets	2	48
Liability Derivatives
Derivatives liabilities at fair value	(473)	(13)
Forward contracts to sell mortgage-related securities
Derivative [Line Items]
Notional Amount	142,808	111,868
Asset Derivatives
Derivative assets	239	0
Liability Derivatives
Derivatives liabilities at fair value	(14)	(117)
Credit enhancement derivatives
Derivative [Line Items]
Notional Amount	25,572	27,269
Asset Derivatives
Derivative assets	48	44
Liability Derivatives
Derivatives liabilities at fair value	(3)	(3)
Other derivatives
Derivative [Line Items]
Notional Amount	3,891	732
Asset Derivatives
Derivative assets	0	0
Liability Derivatives
Derivatives liabilities at fair value	$ (84)	$ (4)