Derivative Instruments Derivatives 2 - FV Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									$ (2,832)	$ (2,110)	$ 422
Net accrual of periodic settlements	$ 7,086	$ 6,656	$ 5,777	$ 5,347	$ 5,922	$ 5,348	$ 5,227	$ 4,796	24,866	21,293	21,273
Pay-fixed swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(2,764)	(3,964)	2,940
Receive-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									2,226	3,685	(1,834)
Basis swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									43	46	(21)
Foreign currency swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									23	24	(51)
Pay-fixed swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(146)	(380)	100
Receive-fixed swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									595	117	(39)
Futures
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(76)	273	38
Risk management derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(360)	(1,032)	72
Net accrual of periodic settlements									(261)	(833)	(1,061)
Mortgage commitment derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(2,654)	(1,043)	324
Credit enhancement derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									$ 182	$ (35)	$ 26