Derivative Instruments Derivatives 2 - FV Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	$ (494)	$ (1,557)	$ (462)	$ (4,290)
Net accrual of periodic settlements	5,002	5,286	10,348	10,055
Pay-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(691)	(2,257)	0	(7,430)
Receive-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	639	1,371	322	4,358
Basis Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	16	14	23	49
Foreign Currency Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	11	(34)	23	(31)
Pay-fixed Swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(48)	4	(48)	29
Receive-fixed Swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(8)	(19)	(26)	(136)
Other
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	3	22	(5)	160
Risk Management Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(302)	(1,190)	(190)	(3,561)
Net accrual of periodic settlements	(224)	(291)	(479)	(560)
Mortgage commitment derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	$ (192)	$ (367)	$ (272)	$ (729)