Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Asset Derivatives [Abstract]
Notional amount	$ 175,667	$ 183,204
Derivative asset, estimated fair value	894	1,485
Netting adjustment	(4,024)	(5,186)
Derivative Liabilities [Abstract]
Notional amount	375,704	408,714
Derivative liability, estimated fair value	(424)	(614)
Netting adjustment	8,650	10,194
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	4,900	5,300
Cash collateral received for derivative instruments	314	245
Risk management derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	113,355	128,628
Derivative asset, estimated fair value	4,020	5,667
Accrued interest receivable	758	749
Netting adjustment	(4,024)	(5,186)
Total net risk management derivatives - Asset	754	1,230
Derivative Liabilities [Abstract]
Notional amount	312,573	344,264
Derivative liability, estimated fair value	(7,939)	(9,451)
Accrued interest payable	(977)	(1,013)
Netting adjustment	8,650	10,194
Total net risk management derivatives - Liability	(266)	(270)
Risk management derivatives [Member] | Pay-fixed Swap [Member]
Asset Derivatives [Abstract]
Notional amount	33,154	41,965
Derivative asset, estimated fair value	267	733
Derivative Liabilities [Abstract]
Notional amount	123,106	123,557
Derivative liability, estimated fair value	(6,920)	(7,125)
Risk management derivatives [Member] | Receive-fixed Swap [Member]
Asset Derivatives [Abstract]
Notional amount	59,796	67,629
Derivative asset, estimated fair value	3,436	4,486
Derivative Liabilities [Abstract]
Notional amount	143,209	157,272
Derivative liability, estimated fair value	(753)	(1,302)
Risk management derivatives [Member] | Basis Swap [Member]
Asset Derivatives [Abstract]
Notional amount	1,864	5,769
Derivative asset, estimated fair value	141	123
Derivative Liabilities [Abstract]
Notional amount	17,100	7,100
Derivative liability, estimated fair value	(15)	(2)
Risk management derivatives [Member] | Foreign Currency Swap [Member]
Asset Derivatives [Abstract]
Notional amount	295	344
Derivative asset, estimated fair value	95	144
Derivative Liabilities [Abstract]
Notional amount	258	273
Derivative liability, estimated fair value	(52)	(30)
Risk management derivatives [Member] | Pay-fixed Swaption [Member]
Asset Derivatives [Abstract]
Notional amount	7,050	11,100
Derivative asset, estimated fair value	45	57
Derivative Liabilities [Abstract]
Notional amount	14,950	26,525
Derivative liability, estimated fair value	(26)	(175)
Risk management derivatives [Member] | Receive-fixed Swaption [Member]
Asset Derivatives [Abstract]
Notional amount	2,000	750
Derivative asset, estimated fair value	8	96
Derivative Liabilities [Abstract]
Notional amount	13,950	29,525
Derivative liability, estimated fair value	(171)	(816)
Risk management derivatives [Member] | Other [Member]
Asset Derivatives [Abstract]
Notional amount	9,196	1,071
Derivative asset, estimated fair value	28	28
Derivative Liabilities [Abstract]
Notional amount	0	12
Derivative liability, estimated fair value	(2)	(1)
Mortgage commitment derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	62,312	54,576
Derivative asset, estimated fair value	140	255
Netting adjustment	0	0
Derivative Liabilities [Abstract]
Notional amount	63,131	64,450
Derivative liability, estimated fair value	(158)	(344)
Netting adjustment	0	0
Mortgage commitment derivatives [Member] | Mortgage Commitments to Purchase Whole Loans [Member]
Asset Derivatives [Abstract]
Notional amount	4,815	6,157
Derivative asset, estimated fair value	9	28
Derivative Liabilities [Abstract]
Notional amount	2,960	428
Derivative liability, estimated fair value	(9)	0
Mortgage commitment derivatives [Member] | Forward Contracts to Purchase Mortgage-related Securities [Member]
Asset Derivatives [Abstract]
Notional amount	31,273	43,533
Derivative asset, estimated fair value	66	223
Derivative Liabilities [Abstract]
Notional amount	19,418	6,112
Derivative liability, estimated fair value	(57)	(8)
Mortgage commitment derivatives [Member] | Forward Contracts to Sell Mortgage-related Securities [Member]
Asset Derivatives [Abstract]
Notional amount	26,224	4,886
Derivative asset, estimated fair value	65	4
Derivative Liabilities [Abstract]
Notional amount	40,753	57,910
Derivative liability, estimated fair value	$ (92)	$ (336)