Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Asset Derivatives [Abstract]
Notional amount	$ 245,315	$ 183,204
Derivative asset, estimated fair value	1,610	1,485
Netting adjustment	(4,417)	(5,186)
Liability Derivatives [Abstract]
Notional amount	327,488	408,714
Derivative liability, estimated fair value	(904)	(614)
Netting adjustment	10,635	10,194
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	6,500	5,300
Cash collateral received for derivative instruments	256	245
Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	176,351	128,628
Derivative asset, estimated fair value	4,808	5,667
Accrued interest receivable, estimated fair value	835	749
Netting adjustment	(4,417)	(5,186)
Derivative Asset	1,226	1,230
Liability Derivatives [Abstract]
Notional amount	237,799	344,264
Derivative liability, estimated fair value	(9,752)	(9,451)
Accrued interest payable, estimated fair value	(1,220)	(1,013)
Netting adjustment	10,635	10,194
Total net risk management derivatives	(337)	(270)
Risk Management Derivatives [Member] | Pay-fixed Swap [Member]
Asset Derivatives [Abstract]
Notional amount	7,557	41,965
Derivative asset, estimated fair value	42	733
Liability Derivatives [Abstract]
Notional amount	151,810	123,557
Derivative liability, estimated fair value	(9,251)	(7,125)
Risk Management Derivatives [Member] | Receive-fixed Swap [Member]
Asset Derivatives [Abstract]
Notional amount	157,472	67,629
Derivative asset, estimated fair value	4,434	4,486
Liability Derivatives [Abstract]
Notional amount	44,981	157,272
Derivative liability, estimated fair value	(145)	(1,302)
Risk Management Derivatives [Member] | Basis Swap [Member]
Asset Derivatives [Abstract]
Notional amount	764	5,769
Derivative asset, estimated fair value	148	123
Liability Derivatives [Abstract]
Notional amount	10,600	7,100
Derivative liability, estimated fair value	(2)	(2)
Risk Management Derivatives [Member] | Foreign Currency Swap [Member]
Asset Derivatives [Abstract]
Notional amount	302	344
Derivative asset, estimated fair value	116	144
Liability Derivatives [Abstract]
Notional amount	265	273
Derivative liability, estimated fair value	(46)	(30)
Risk Management Derivatives [Member] | Pay-fixed Swaption [Member]
Asset Derivatives [Abstract]
Notional amount	6,300	11,100
Derivative asset, estimated fair value	43	57
Liability Derivatives [Abstract]
Notional amount	13,950	26,525
Derivative liability, estimated fair value	(24)	(175)
Risk Management Derivatives [Member] | Receive-fixed Swaption [Member]
Asset Derivatives [Abstract]
Notional amount	0	750
Derivative asset, estimated fair value	0	96
Liability Derivatives [Abstract]
Notional amount	14,200	29,525
Derivative liability, estimated fair value	(283)	(816)
Risk Management Derivatives [Member] | Other [Member]
Asset Derivatives [Abstract]
Notional amount	3,956	1,071
Derivative asset, estimated fair value	25	28
Liability Derivatives [Abstract]
Notional amount	1,993	12
Derivative liability, estimated fair value	(1)	(1)
Mortgage commitment derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	68,964	54,576
Derivative asset, estimated fair value	384	255
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	89,689	64,450
Derivative liability, estimated fair value	(567)	(344)
Netting adjustment	0	0
Mortgage commitment derivatives [Member] | Mortgage Commitments to Purchase Whole Loans [Member]
Asset Derivatives [Abstract]
Notional amount	9,595	6,157
Derivative asset, estimated fair value	57	28
Liability Derivatives [Abstract]
Notional amount	28	428
Derivative liability, estimated fair value	0	0
Mortgage commitment derivatives [Member] | Forward Contracts to Purchase Mortgage-related Securities [Member]
Asset Derivatives [Abstract]
Notional amount	57,746	43,533
Derivative asset, estimated fair value	326	223
Liability Derivatives [Abstract]
Notional amount	2,245	6,112
Derivative liability, estimated fair value	(4)	(8)
Mortgage commitment derivatives [Member] | Forward Contracts to Sell Mortgage-related Securities [Member]
Asset Derivatives [Abstract]
Notional amount	1,623	4,886
Derivative asset, estimated fair value	1	4
Liability Derivatives [Abstract]
Notional amount	87,416	57,910
Derivative liability, estimated fair value	$ (563)	$ (336)