Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Asset Derivatives [Abstract]
Notional amount	$ 280,038	$ 175,667
Derivative asset, estimated fair value	775	894
Netting adjustment	(7,530)	(4,024)
Liability Derivatives [Abstract]
Notional amount	312,686	375,704
Derivative liability, estimated fair value	(1,135)	(424)
Netting adjustment	14,269	8,650
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	7,100	4,900
Cash collateral received for derivative instruments	345	314
Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	189,311	113,355
Derivative asset, estimated fair value	6,849	4,020
Accrued interest receivable	819	758
Netting adjustment	(7,530)	(4,024)
Total net risk management derivatives - Asset	138	754
Liability Derivatives [Abstract]
Notional amount	191,226	312,573
Derivative liability, estimated fair value	(13,401)	(7,939)
Accrued interest payable	(1,045)	(977)
Netting adjustment	14,269	8,650
Total net risk management derivatives - Liability	(177)	(266)
Risk Management Derivatives [Member] | Pay-fixed Swap [Member]
Asset Derivatives [Abstract]
Notional amount	325	33,154
Derivative asset, estimated fair value	1	267
Liability Derivatives [Abstract]
Notional amount	156,864	123,106
Derivative liability, estimated fair value	(13,141)	(6,920)
Risk Management Derivatives [Member] | Receive-fixed Swap [Member]
Asset Derivatives [Abstract]
Notional amount	170,271	59,796
Derivative asset, estimated fair value	6,516	3,436
Liability Derivatives [Abstract]
Notional amount	11,113	143,209
Derivative liability, estimated fair value	(5)	(753)
Risk Management Derivatives [Member] | Basis Swap [Member]
Asset Derivatives [Abstract]
Notional amount	1,864	1,864
Derivative asset, estimated fair value	189	141
Liability Derivatives [Abstract]
Notional amount	17,100	17,100
Derivative liability, estimated fair value	(15)	(15)
Risk Management Derivatives [Member] | Foreign Currency Swap [Member]
Asset Derivatives [Abstract]
Notional amount	222	295
Derivative asset, estimated fair value	80	95
Liability Derivatives [Abstract]
Notional amount	233	258
Derivative liability, estimated fair value	(81)	(52)
Risk Management Derivatives [Member] | Pay-fixed Swaption [Member]
Asset Derivatives [Abstract]
Notional amount	6,880	7,050
Derivative asset, estimated fair value	36	45
Liability Derivatives [Abstract]
Notional amount	2,350	14,950
Derivative liability, estimated fair value	(4)	(26)
Risk Management Derivatives [Member] | Receive-fixed Swaption [Member]
Asset Derivatives [Abstract]
Notional amount	0	2,000
Derivative asset, estimated fair value	0	8
Liability Derivatives [Abstract]
Notional amount	3,430	13,950
Derivative liability, estimated fair value	(154)	(171)
Risk Management Derivatives [Member] | Other [Member]
Asset Derivatives [Abstract]
Notional amount	9,749	9,196
Derivative asset, estimated fair value	27	28
Liability Derivatives [Abstract]
Notional amount	136	0
Derivative liability, estimated fair value	(1)	(2)
Mortgage commitment derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	90,727	62,312
Derivative asset, estimated fair value	637	140
Netting adjustment	0	0
Liability Derivatives [Abstract]
Notional amount	121,460	63,131
Derivative liability, estimated fair value	(958)	(158)
Netting adjustment	0	0
Mortgage commitment derivatives [Member] | Mortgage Commitments to Purchase Whole Loans [Member]
Asset Derivatives [Abstract]
Notional amount	13,157	4,815
Derivative asset, estimated fair value	99	9
Liability Derivatives [Abstract]
Notional amount	29	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	75,635	31,273
Derivative asset, estimated fair value	533	66
Liability Derivatives [Abstract]
Notional amount	4,024	19,418
Derivative liability, estimated fair value	(9)	(57)
Mortgage commitment derivatives [Member] | Forward Contracts to Sell Mortgage-related Securities [Member]
Asset Derivatives [Abstract]
Notional amount	1,935	26,224
Derivative asset, estimated fair value	5	65
Liability Derivatives [Abstract]
Notional amount	117,407	40,753
Derivative liability, estimated fair value	$ (949)	$ (92)