Derivative Instruments Derivatives 2 - FV Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	$ (396)	$ (149)	$ (858)	$ (4,439)
Net accrual of periodic settlements	5,274	5,435	15,622	15,490
Pay-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	300	1,386	300	(6,044)
Receive-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(202)	(1,020)	120	3,338
Basis Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	1	2	24	51
Foreign Currency Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	13	(6)	36	(37)
Pay-fixed Swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(40)	(3)	(88)	26
Receive-fixed Swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(8)	10	(34)	(126)
Other
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	11	(7)	6	153
Risk Management Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(148)	67	(338)	(3,494)
Net accrual of periodic settlements	(223)	(295)	(702)	(855)
Mortgage commitment derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	$ (248)	$ (216)	$ (520)	$ (945)