Derivative Instruments Derivatives 2 - FV Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	$ 360	$ (396)	$ 1,185	$ (858)
Net accrual of periodic settlements	5,369	5,274	15,978	15,622
Pay-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	1,034	300	4,784	300
Receive-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(524)	(202)	(3,508)	120
Basis Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(5)	1	(31)	24
Foreign Currency Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(10)	13	(35)	36
Pay-fixed Swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	67	(40)	232	(88)
Receive-fixed Swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(34)	(8)	(72)	(34)
Other
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	(1)	11	(5)	6
Risk Management Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	242	(148)	579	(338)
Net accrual of periodic settlements	(285)	(223)	(786)	(702)
Mortgage commitment derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net	$ 118	$ (248)	$ 606	$ (520)