Derivative Instruments - FV Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	$ 13	$ (294)	$ 654	$ (2,228)
Net contractual interest income (expense) on interest-rate swaps	6,972	6,656	22,000	17,780
Interest income on mortgage loans	24,798	25,810	73,083	81,755
Long-term debt	(18,009)	(19,378)	(51,646)	(64,815)
Hedged Asset, Fair Value Hedge	150,829		150,829
Hedged Liability, Fair Value Hedge	(72,497)		(72,497)
Hedged Asset, Fair Value Hedge, Cumulative Increase (Decrease)	66		66
Hedged Liability, Fair Value Hedge, Cumulative Increase (Decrease)	946		946
Hedged Asset, Discontinued Fair Value Hedge, Cumulative Increase (Decrease)	66		66
Hedged Liability, Discontinued Fair Value Hedge, Cumulative Increase (Decrease)	946		946
Hedged Asset, Fair Value Hedge, Last-of-Layer, Cumulative Increase (Decrease)	36,424		36,424
Hedged Asset, Fair Value Hedge, Last-of-Layer, Amount	2,548		2,548
Pay-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	343	634	1,855	(3,489)
Receive-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(209)	(550)	(1,307)	2,984
Basis Swap
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(12)	(5)	(39)	68
Foreign Currency Swap
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(19)	23	(23)	(11)
Pay-fixed Swaption
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	6	2	55	(159)
Receive-fixed Swaption
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(14)	(60)	(223)	597
Futures
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	0	0	1	(75)
Risk Management Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	93	(2)	313	(301)
Net contractual interest income (expense) on interest-rate swaps	(2)	(46)	(6)	(216)
Mortgage commitment derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(25)	(672)	504	(2,327)
Credit enhancement derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Total derivatives fair value gains (losses), net	(55)	$ 380	(163)	$ 400
Interest rate risk on held-for-investment mortgage loan | Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) in hedged item	(1)		69
Discontinued hedge related basis adjustment amortization	(3)		(3)
Change in unrealized gain (loss) in derivatives designated as hedging instruments	(1)		(71)
Interest accruals on hedging instruments	(4)		(9)
Total effect of fair value hedges	(9)		(14)
Interest rate risk on debt | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) in hedged item	195		1,000
Discontinued hedge related basis adjustment amortization	(20)		(54)
Change in unrealized gain (loss) in derivatives designated as hedging instruments	(191)		(982)
Interest accruals on hedging instruments	65		178
Total effect of fair value hedges	$ 49		$ 142