Derivative Instruments Derivatives 1 - Notional and FV Position (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Asset Derivatives [Abstract]
Notional amount	$ 183,204,000,000	$ 245,573,000,000
Derivative asset, estimated fair value	1,485,000,000	2,073,000,000
Netting adjustment	(5,186,000,000)	(8,422,000,000)
Derivative Liabilities [Abstract]
Notional amount	408,714,000,000	380,094,000,000
Derivative liability, estimated fair value	(614,000,000)	(1,469,000,000)
Netting adjustment	10,194,000,000
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	5,300,000,000	2,000,000,000
Cash collateral received for derivative instruments	245,000,000	1,000,000,000
Risk management derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	128,628,000,000	205,736,000,000
Derivative asset, estimated fair value	5,667,000,000	9,444,000,000
Accrued interest receivable, estimated fair value	749,000,000	786,000,000
Netting adjustment	(5,186,000,000)	(8,422,000,000)
Total net risk management derivatives, estimated fair value	1,230,000,000	1,808,000,000
Derivative Liabilities [Abstract]
Notional amount	344,264,000,000	346,994,000,000
Derivative liability, estimated fair value	(9,451,000,000)	(9,695,000,000)
Accrued interest receivable (payable), estimated fair value	(1,013,000,000)	(930,000,000)
Netting adjustment	10,194,000,000	9,370,000,000
Total net risk management derivatives, estimated fair value	(270,000,000)	(1,255,000,000)
Risk management derivatives [Member] | Pay-fixed Swap [Member]
Asset Derivatives [Abstract]
Notional amount	41,965,000,000	68,637,000,000
Derivative asset, estimated fair value	733,000,000	5,378,000,000
Derivative Liabilities [Abstract]
Notional amount	123,557,000,000	93,428,000,000
Derivative liability, estimated fair value	(7,125,000,000)	(4,759,000,000)
Risk management derivatives [Member] | Receive-fixed Swap [Member]
Asset Derivatives [Abstract]
Notional amount	67,629,000,000	67,527,000,000
Derivative asset, estimated fair value	4,486,000,000	3,320,000,000
Derivative Liabilities [Abstract]
Notional amount	157,272,000,000	156,250,000,000
Derivative liability, estimated fair value	(1,302,000,000)	(3,813,000,000)
Risk management derivatives [Member] | Basis Swap [Member]
Asset Derivatives [Abstract]
Notional amount	5,769,000,000	27,014,000,000
Derivative asset, estimated fair value	123,000,000	36,000,000
Derivative Liabilities [Abstract]
Notional amount	7,100,000,000	600,000,000
Derivative liability, estimated fair value	(2,000,000)	0
Risk management derivatives [Member] | Foreign Currency Swap [Member]
Asset Derivatives [Abstract]
Notional amount	344,000,000	389,000,000
Derivative asset, estimated fair value	144,000,000	120,000,000
Derivative Liabilities [Abstract]
Notional amount	273,000,000	653,000,000
Derivative liability, estimated fair value	(30,000,000)	(38,000,000)
Risk management derivatives [Member] | Pay-fixed Swaption [Member]
Asset Derivatives [Abstract]
Notional amount	11,100,000,000	33,400,000,000
Derivative asset, estimated fair value	57,000,000	445,000,000
Derivative Liabilities [Abstract]
Notional amount	26,525,000,000	48,025,000,000
Derivative liability, estimated fair value	(175,000,000)	(600,000,000)
Risk management derivatives [Member] | Receive-fixed Swaption [Member]
Asset Derivatives [Abstract]
Notional amount	750,000,000	8,000,000,000
Derivative asset, estimated fair value	96,000,000	117,000,000
Derivative Liabilities [Abstract]
Notional amount	29,525,000,000	48,025,000,000
Derivative liability, estimated fair value	(816,000,000)	(484,000,000)
Risk management derivatives [Member] | Other [Member]
Asset Derivatives [Abstract]
Notional amount	1,071,000,000	769,000,000
Derivative asset, estimated fair value	28,000,000	28,000,000
Derivative Liabilities [Abstract]
Notional amount	12,000,000	13,000,000
Derivative liability, estimated fair value	(1,000,000)	(1,000,000)
Mortgage commitment derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	54,576,000,000	39,837,000,000
Derivative asset, estimated fair value	255,000,000	265,000,000
Netting adjustment	0	0
Derivative Liabilities [Abstract]
Notional amount	64,450,000,000	33,100,000,000
Derivative liability, estimated fair value	(344,000,000)	(214,000,000)
Netting adjustment	0	0
Mortgage commitment derivatives [Member] | Mortgage Commitments to Purchase Whole Loans [Member]
Asset Derivatives [Abstract]
Notional amount	6,157,000,000	1,138,000,000
Derivative asset, estimated fair value	28,000,000	1,000,000
Derivative Liabilities [Abstract]
Notional amount	428,000,000	4,353,000,000
Derivative liability, estimated fair value	0	(31,000,000)
Mortgage commitment derivatives [Member] | Forward Contracts to Purchase Mortgage-related Securities [Member]
Asset Derivatives [Abstract]
Notional amount	43,533,000,000	3,276,000,000
Derivative asset, estimated fair value	223,000,000	4,000,000
Derivative Liabilities [Abstract]
Notional amount	6,112,000,000	20,861,000,000
Derivative liability, estimated fair value	(8,000,000)	(168,000,000)
Mortgage commitment derivatives [Member] | Forward Contracts to Sell Mortgage-related Securities [Member]
Asset Derivatives [Abstract]
Notional amount	4,886,000,000	35,423,000,000
Derivative asset, estimated fair value	4,000,000	260,000,000
Derivative Liabilities [Abstract]
Notional amount	57,910,000,000	7,886,000,000
Derivative liability, estimated fair value	$ (336,000,000)	$ (15,000,000)