Derivative Instruments - FV Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	$ (175)	$ (860)	$ (576)	$ 124
Net contractual interest income (expense) on interest-rate swaps	7,184	7,275	21,340	21,566
Interest income on mortgage loans	38,344	36,390	113,436	107,223
Long-term debt	(32,639)	(30,600)	(96,702)	(90,057)
Hedged asset, carrying amount	1,240,556		1,240,556		$ 1,109,445
Hedged asset, total basis adjustments	(40)		(40)		(816)
Hedged asset, discontinued fair value, remaining adjustments	(40)		(40)		(816)
Closed portfolio, amortized cost	283,665		283,665		813,536
Closed portfolio, designated UPB	32,952		32,952		26,825
Hedged liability, carrying amount	(32,642)		(32,642)		(47,849)
Hedged liability, total basis adjustments	2,498		2,498		3,390
Hedged liability, discontinued fair value, remaining adjustments	2,498		2,498		$ 3,390
Pay-fixed
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(43)	(2,225)	(1,253)	(626)
Receive-fixed
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	362	2,225	1,979	1,738
Basis
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	7	17	8	14
Foreign currency
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(9)	19	23	8
Pay-fixed
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(79)	(29)	(94)	15
Receive-fixed
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(26)	3	(35)	6
Futures
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(1)	(2)	0	0
Risk Management Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	117	(255)	133	442
Net contractual interest income (expense) on interest-rate swaps	(94)	(263)	(495)	(713)
Mortgage commitment derivatives fair value gains (losses), net
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(295)	(567)	(684)	(266)
Credit enhancement derivatives fair value gains (losses), net
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	3	(38)	(25)	(52)
Interest rate risk on held-for-investment mortgage loan | Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) in hedged item	100	730	747	368
Discontinued hedge related basis adjustment amortization	6	3	29	29
Change in unrealized gain (loss) in derivatives designated as hedging instruments	(89)	(725)	(732)	(410)
Interest accruals on hedging instruments	61	84	170	226
Total effect of fair value hedges	78	92	214	213
Interest rate risk on debt | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) in hedged item	15	(506)	(259)	51
Discontinued hedge related basis adjustment amortization	(193)	(213)	(633)	(641)
Change in unrealized gain (loss) in derivatives designated as hedging instruments	(20)	519	258	86
Interest accruals on hedging instruments	(25)	(93)	(70)	(373)
Total effect of fair value hedges	$ (223)	$ (293)	$ (704)	$ (877)