Fair Value Disclosures - Schedule of Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets:
Trading securities	$ 633	$ 748
AFS securities	24,547	26,926
LHFS	1,099	1,716
MSRs	1,056	1,052
Derivative assets	443	822
Private equity investments	404	362
Total assets	28,182	31,626
Liabilities:
Derivative liabilities	714	1,003
Securities sold short	120	137
Total liabilities	834	1,140
Level 1
Assets:
Trading securities	363	324
AFS securities	6	8
LHFS	0	0
MSRs	0	0
Derivative assets	0	0
Private equity investments	0	0
Total assets	369	332
Liabilities:
Derivative liabilities	0	0
Securities sold short	0	0
Level 2
Assets:
Trading securities	270	424
AFS securities	24,109	26,411
LHFS	1,099	1,716
MSRs	0	0
Derivative assets	437	815
Private equity investments	0	0
Total assets	25,915	29,366
Liabilities:
Derivative liabilities	711	983
Securities sold short	120	137
Total liabilities	831	1,120
Level 3
Assets:
Trading securities	0	0
AFS securities	432	507
LHFS	0	0
MSRs	1,056	1,052
Derivative assets	6	7
Private equity investments	404	362
Total assets	1,898	1,928
Liabilities:
Derivative liabilities	3	20
Securities sold short	0	0
Total liabilities	3	20
U.S. Treasury
Assets:
AFS securities	2,291	2,587
U.S. Treasury | Level 1
Assets:
AFS securities	0	0
U.S. Treasury | Level 2
Assets:
AFS securities	2,291	2,587
U.S. Treasury | Level 3
Assets:
AFS securities	0	0
GSE
Assets:
AFS securities	179	180
GSE | Level 1
Assets:
AFS securities	0	0
GSE | Level 2
Assets:
AFS securities	179	180
GSE | Level 3
Assets:
AFS securities	0	0
Agency MBS
Assets:
AFS securities	20,101	21,264
Agency MBS | Level 1
Assets:
AFS securities	0	0
Agency MBS | Level 2
Assets:
AFS securities	20,101	21,264
Agency MBS | Level 3
Assets:
AFS securities	0	0
States and political subdivisions
Assets:
AFS securities	1,392	2,205
States and political subdivisions | Level 1
Assets:
AFS securities	0	0
States and political subdivisions | Level 2
Assets:
AFS securities	1,392	2,205
States and political subdivisions | Level 3
Assets:
AFS securities	0	0
Non-agency MBS
Assets:
AFS securities	576	679
Non-agency MBS | Level 1
Assets:
AFS securities	0	0
Non-agency MBS | Level 2
Assets:
AFS securities	144	172
Non-agency MBS | Level 3
Assets:
AFS securities	432	507
Other
Assets:
AFS securities	8	11
Other | Level 1
Assets:
AFS securities	6	8
Other | Level 2
Assets:
AFS securities	2	3
Other | Level 3
Assets:
AFS securities	0	0
Interest rate contracts
Assets:
Derivative assets	440	814
Liabilities:
Derivative liabilities	708	998
Interest rate contracts | Level 1
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Interest rate contracts | Level 2
Assets:
Derivative assets	434	807
Liabilities:
Derivative liabilities	705	978
Interest rate contracts | Level 3
Assets:
Derivative assets	6	7
Liabilities:
Derivative liabilities	3	20
Foreign exchange contracts
Assets:
Derivative assets	3	8
Liabilities:
Derivative liabilities	6	5
Foreign exchange contracts | Level 1
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Foreign exchange contracts | Level 2
Assets:
Derivative assets	3	8
Liabilities:
Derivative liabilities	6	5
Foreign exchange contracts | Level 3
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	$ 0	$ 0