Derivative Instruments Derivatives 2 - FV Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended								6 Months Ended	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									$ (1,185)	$ (2,110)	$ 422
Net accrual of periodic settlements	$ 5,850	$ 5,229	$ 5,150	$ 4,733	$ 4,973	$ 5,369	$ 5,377	$ 5,232		20,962	20,951	$ 20,733
Pay-fixed swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									1,296	(3,964)	2,940
Receive-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(851)	3,685	(1,834)
Basis swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									21	46	(21)
Foreign currency swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									49	24	(51)
Pay-fixed swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(161)	(380)	100
Receive-fixed swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(60)	117	(39)
Futures
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									22	273	38
Risk management derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(573)	(1,032)	72
Net accrual of periodic settlements									(889)	(833)	(1,061)
Mortgage commitment derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(603)	(1,043)	324
Credit enhancement derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									$ (9)	$ (35)	$ 26