Derivative Instruments - FV Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains, net	$ 1,353	$ 1,148
Net contractual interest expense on interest-rate swaps	7,399	6,742
Interest income on mortgage loans	27,142	23,353
Long-term debt	(19,940)	(16,817)
Hedged asset, carrying amount	208,820		$ 174,080
Hedged asset, total basis adjustments	(104)		134
Hedged asset, discontinued fair value, remaining adjustments	(104)		134
Closed portfolio, amortized cost	62,004		56,786
Closed portfolio, designated UPB	5,379		4,389
Hedged liability, carrying amount	(76,619)		(72,174)
Hedged liability, total basis adjustments	2,838		1,281
Hedged liability, discontinued fair value, remaining adjustments	2,838		$ 1,281
Pay-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains, net	2,125	2,207
Receive-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains, net	(2,260)	(1,855)
Basis Swap
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains, net	(68)	(46)
Foreign Currency Swap
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains, net	(24)	(8)
Pay-fixed Swaption
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains, net	44	107
Receive-fixed Swaption
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains, net	(3)	(239)
Futures
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains, net	0	1
Risk Management Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains, net	(197)	156
Net contractual interest expense on interest-rate swaps	(11)	(11)
Mortgage commitment derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains, net	1,572	1,082
Credit enhancement derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains, net	(22)	(90)
Interest rate risk on held-for-investment mortgage loan | Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) in hedged item	(238)	(36)
Discontinued hedge related basis adjustment amortization	0	0
Change in unrealized gain (loss) in derivatives designated as hedging instruments	227	36
Interest accruals on hedging instruments	(8)	0
Total effect of fair value hedges	(19)	0
Interest rate risk on debt | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) in hedged item	1,623	1,195
Discontinued hedge related basis adjustment amortization	(65)	(13)
Change in unrealized gain (loss) in derivatives designated as hedging instruments	(1,524)	(1,214)
Interest accruals on hedging instruments	47	54
Total effect of fair value hedges	$ 81	$ 22