Fair Value Disclosures - Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Assets
AFS securities	$ 23,919	$ 24,547
LHFS at fair value	1,615	1,099
MSRs	1,143	1,056
Trading and equity securities	820	633
Derivative assets	192	443
Private equity investments	399	404
Total assets	28,088	28,182
Liabilities [Abstract]
Derivative liabilities	395	714
Securities sold short	235	120
Total liabilities	630	834
Level 1
Assets
AFS securities	0	6
LHFS at fair value	0	0
MSRs	0	0
Trading and equity securities	380	363
Derivative assets	0	0
Private equity investments	0	0
Total assets	380	369
Liabilities [Abstract]
Derivative liabilities	0	0
Securities sold short	0	0
Total liabilities	0	0
Level 2
Assets
AFS securities	23,494	24,109
LHFS at fair value	1,615	1,099
MSRs	0	0
Trading and equity securities	440	270
Derivative assets	185	437
Private equity investments	0	0
Total assets	25,734	25,915
Liabilities [Abstract]
Derivative liabilities	392	711
Securities sold short	235	120
Total liabilities	627	831
Level 3
Assets
AFS securities	425	432
LHFS at fair value	0	0
MSRs	1,143	1,056
Trading and equity securities		0
Derivative assets	7	6
Private equity investments	399	404
Total assets	1,974	1,898
Liabilities [Abstract]
Derivative liabilities	3	3
Securities sold short	0	0
Total liabilities	3	3
U.S. Treasury \| Level 1
Assets
AFS securities	0	0
U.S. Treasury \| Level 2
Assets
AFS securities	2,323	2,291
U.S. Treasury \| Level 3
Assets
AFS securities	0	0
GSE \| Level 1
Assets
AFS securities	0	0
GSE \| Level 2
Assets
AFS securities	175	179
GSE \| Level 3
Assets
AFS securities	0	0
Agency MBS \| Level 1
Assets
AFS securities	0	0
Agency MBS \| Level 2
Assets
AFS securities	19,848	20,101
Agency MBS \| Level 3
Assets
AFS securities	0	0
States and political subdivisions \| Level 1
Assets
AFS securities	0	0
States and political subdivisions \| Level 2
Assets
AFS securities	980	1,392
States and political subdivisions \| Level 3
Assets
AFS securities	0	0
Non-agency MBS \| Level 1
Assets
AFS securities	0	0
Non-agency MBS \| Level 2
Assets
AFS securities	129	144
Non-agency MBS \| Level 3
Assets
AFS securities	425	432
Other \| Level 1
Assets
AFS securities		6
Other \| Level 2
Assets
AFS securities	39	2
Other \| Level 3
Assets
AFS securities	$ 0	$ 0

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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