Derivative Instruments Derivatives 2 - FV Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									$ (1,513)	$ (5,764)	$ 3,280
Accrual of periodic settlements	$ 5,077	$ 5,588	$ 5,677	$ 5,067	$ 5,142	$ 5,184	$ 4,904	$ 4,738	21,409	19,968	22,404
Risk management derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(1,120)	(4,624)	2,779
Risk management derivatives [Member] | Pay-fixed Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(746)	(7,703)	14,393
Accrual of periodic settlements									(3,602)	(3,712)	(4,463)
Risk management derivatives [Member] | Receive-fixed Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									625	4,229	(10,721)
Accrual of periodic settlements									2,603	2,600	3,632
Risk management derivatives [Member] | Basis Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									4	85	(115)
Risk management derivatives [Member] | Foreign Currency Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(60)	27	(101)
Risk management derivatives [Member] | Pay-fixed Swaption [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									135	(4)	(238)
Risk management derivatives [Member] | Receive-fixed Swaption [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(93)	(197)	307
Risk management derivatives [Member] | Other [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(25)	1	21
Accrual of periodic settlements									39	50	64
Mortgage commitment derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									$ (393)	$ (1,140)	$ 501