Derivative Instruments - FV Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	$ 672	$ (338)
Net contractual interest expense on interest-rate swaps	7,023	6,786
Interest income on mortgage loans	35,216	32,137
Long-term debt	(29,580)	(26,665)
Hedged asset, carrying amount	687,058		$ 449,137
Hedged asset, total basis adjustments	(500)		(174)
Hedged asset, discontinued fair value, remaining adjustments	(500)		(174)
Closed portfolio, amortized cost	454,310		218,419
Closed portfolio, designated UPB	9,482		9,955
Hedged liability, carrying amount	(56,930)		(59,462)
Hedged liability, total basis adjustments	3,973		3,751
Hedged liability, discontinued fair value, remaining adjustments	3,973		$ 3,751
Pay-fixed
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	1,362	(1,590)
Receive-fixed
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(696)	1,572
Basis
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	1	13
Foreign currency
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(8)	8
Pay-fixed
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	23	(33)
Receive-fixed
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(4)	(1)
Futures
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	1	0
Risk Management Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	480	(209)
Net contractual interest expense on interest-rate swaps	(199)	(178)
Mortgage commitment derivatives fair value gains (losses), net
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	207	(114)
Credit enhancement derivatives fair value losses, net
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(15)	(15)
Interest rate risk on held-for-investment mortgage loan | Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) in hedged item	(334)	177
Discontinued hedge related basis adjustment amortization	8	11
Change in unrealized gain (loss) in derivatives designated as hedging instruments	309	(214)
Interest accruals on hedging instruments	66	26
Total effect of fair value hedges	49	0
Interest rate risk on debt | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) in hedged item	428	(239)
Discontinued hedge related basis adjustment amortization	(206)	(196)
Change in unrealized gain (loss) in derivatives designated as hedging instruments	(355)	432
Interest accruals on hedging instruments	(167)	(229)
Total effect of fair value hedges	$ (300)	$ (232)