Derivative Instruments - FV Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	$ (860)	$ 803	$ 124	$ 1,440
Net contractual interest income (expense) on interest-rate swaps	7,275	7,220	21,566	21,041
Interest income on mortgage loans	36,390	33,711	107,223	98,503
Long-term debt	(30,600)	(27,994)	(90,057)	(81,781)
Hedged asset, carrying amount	856,849		856,849		$ 449,137
Hedged asset, total basis adjustments	223		223		(174)
Hedged asset, discontinued fair value, remaining adjustments	223		223		(174)
Closed portfolio, amortized cost	440,276		440,276		218,419
Closed portfolio, designated UPB	18,435		18,435		9,955
Hedged liability, carrying amount	(50,473)		(50,473)		(59,462)
Hedged liability, total basis adjustments	3,161		3,161		3,751
Hedged liability, discontinued fair value, remaining adjustments	3,161		3,161		$ 3,751
Pay-fixed
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(2,225)	1,349	(626)	1,617
Receive-fixed
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	2,225	(1,040)	1,738	(478)
Basis
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	17	(22)	14	6
Foreign currency
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	19	(12)	8	(2)
Pay-fixed
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(29)	95	15	74
Receive-fixed
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	3	(13)	6	(16)
Futures
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(2)	1	0	2
Risk Management Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(255)	165	442	704
Net contractual interest income (expense) on interest-rate swaps	(263)	(193)	(713)	(499)
Mortgage commitment derivatives fair value gains (losses), net
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(567)	591	(266)	675
Credit enhancement derivatives fair value gains (losses), net
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(38)	47	(52)	61
Interest rate risk on held-for-investment mortgage loan | Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) in hedged item	730	(544)	368	(511)
Discontinued hedge related basis adjustment amortization	3	14	29	34
Change in unrealized gain (loss) in derivatives designated as hedging instruments	(725)	560	(410)	478
Interest accruals on hedging instruments	84	36	226	89
Total effect of fair value hedges	92	66	213	90
Interest rate risk on debt | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) in hedged item	(506)	176	51	606
Discontinued hedge related basis adjustment amortization	(213)	(223)	(641)	(618)
Change in unrealized gain (loss) in derivatives designated as hedging instruments	519	(66)	86	(137)
Interest accruals on hedging instruments	(93)	(191)	(373)	(713)
Total effect of fair value hedges	$ (293)	$ (304)	$ (877)	$ (862)