Derivative Instruments Derivatives 2 - FV Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	$ 863	$ 32
Net accrual of periodic settlements	5,232	5,346
Pay-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	2,783	691
Receive-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(2,387)	(317)
Basis Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(23)	7
Foreign Currency Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	16	12
Pay-fixed Swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	129	0
Receive-fixed Swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(16)	(18)
Other
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	12	(8)
Risk Management Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	299	112
Net accrual of periodic settlements	(215)	(255)
Mortgage commitment derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	$ 564	$ (80)