Derivative Instruments Derivatives 2 - FV Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	$ 32	$ (2,733)
Net accrual of periodic settlements	5,346	4,769
Pay-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	691	(5,173)
Receive-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(317)	2,987
Basis Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	7	35
Foreign Currency Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	12	3
Pay-fixed Swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	0	25
Receive-fixed Swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(18)	(117)
Other [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(8)	138
Risk Management Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	112	(2,371)
Net accrual of periodic settlements	(255)	(269)
Mortgage commitment derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	$ (80)	$ (362)