Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Asset Derivatives [Abstract]
Notional amount	$ 255,457	$ 175,667
Derivative asset, estimated fair value	700	894
Netting adjustment	(6,724)	(4,024)
Liability Derivatives [Abstract]
Notional amount	351,825	375,704
Derivative liability, estimated fair value	(1,116)	(424)
Netting adjustment	12,598	8,650
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	6,200	4,900
Cash collateral received for derivatives instruments	365	314
Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	165,431	113,355
Derivative asset, estimated fair value	5,997	4,020
Accrued interest receivable	917	758
Netting adjustment	(6,724)	(4,024)
Total net risk management derivatives - Asset	190	754
Liability Derivatives [Abstract]
Notional amount	242,562	312,573
Derivative liability, estimated fair value	(11,882)	(7,939)
Accrued interest payable	(1,227)	(977)
Netting adjustment	12,598	8,650
Total net risk management derivatives - Liability	(511)	(266)
Risk Management Derivatives [Member] | Pay-fixed Swap [Member]
Asset Derivatives [Abstract]
Notional amount	525	33,154
Derivative asset, estimated fair value	0	267
Liability Derivatives [Abstract]
Notional amount	153,975	123,106
Derivative liability, estimated fair value	(11,582)	(6,920)
Risk Management Derivatives [Member] | Receive-fixed Swap [Member]
Asset Derivatives [Abstract]
Notional amount	142,656	59,796
Derivative asset, estimated fair value	5,651	3,436
Liability Derivatives [Abstract]
Notional amount	60,286	143,209
Derivative liability, estimated fair value	(53)	(753)
Risk Management Derivatives [Member] | Basis Swap [Member]
Asset Derivatives [Abstract]
Notional amount	1,864	1,864
Derivative asset, estimated fair value	174	141
Liability Derivatives [Abstract]
Notional amount	17,100	17,100
Derivative liability, estimated fair value	(14)	(15)
Risk Management Derivatives [Member] | Foreign Currency Swap [Member]
Asset Derivatives [Abstract]
Notional amount	263	295
Derivative asset, estimated fair value	98	95
Liability Derivatives [Abstract]
Notional amount	251	258
Derivative liability, estimated fair value	(61)	(52)
Risk Management Derivatives [Member] | Pay-fixed Swaption [Member]
Asset Derivatives [Abstract]
Notional amount	9,800	7,050
Derivative asset, estimated fair value	43	45
Liability Derivatives [Abstract]
Notional amount	4,600	14,950
Derivative liability, estimated fair value	(7)	(26)
Risk Management Derivatives [Member] | Receive-fixed Swaption [Member]
Asset Derivatives [Abstract]
Notional amount	2,000	2,000
Derivative asset, estimated fair value	4	8
Liability Derivatives [Abstract]
Notional amount	6,350	13,950
Derivative liability, estimated fair value	(164)	(171)
Risk Management Derivatives [Member] | Other [Member]
Asset Derivatives [Abstract]
Notional amount	8,323	9,196
Derivative asset, estimated fair value	27	28
Liability Derivatives [Abstract]
Notional amount	0	0
Derivative liability, estimated fair value	(1)	(2)
Mortgage commitment derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	90,026	62,312
Derivative asset, estimated fair value	510	140
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	109,263	63,131
Derivative liability, estimated fair value	(605)	(158)
Netting adjustment	0	0
Mortgage commitment derivatives [Member] | Mortgage Commitments to Purchase Whole Loans [Member]
Asset Derivatives [Abstract]
Notional amount	10,507	4,815
Derivative asset, estimated fair value	48	9
Liability Derivatives [Abstract]
Notional amount	211	2,960
Derivative liability, estimated fair value	0	(9)
Mortgage commitment derivatives [Member] | Forward Contracts to Purchase Mortgage-related Securities [Member]
Asset Derivatives [Abstract]
Notional amount	77,994	31,273
Derivative asset, estimated fair value	457	66
Liability Derivatives [Abstract]
Notional amount	1,893	19,418
Derivative liability, estimated fair value	(4)	(57)
Mortgage commitment derivatives [Member] | Forward Contracts to Sell Mortgage-related Securities [Member]
Asset Derivatives [Abstract]
Notional amount	1,525	26,224
Derivative asset, estimated fair value	5	65
Liability Derivatives [Abstract]
Notional amount	107,159	40,753
Derivative liability, estimated fair value	$ (601)	$ (92)