Fair Value Disclosures - Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Assets
AFS securities	$ 24,286	$ 24,547
LHFS at fair value	1,022	1,099
MSRs	1,179	1,056
Trading and equity securities	1,136	633
Derivative assets	186	443
Private equity investments	427	404
Total assets	28,236	28,182
Liabilities [Abstract]
Derivative liabilities	439	714
Securities sold short	145	120
Total liabilities	584	834
Level 1
Assets
AFS securities	0	6
LHFS at fair value	0	0
MSRs	0	0
Trading and equity securities	464	363
Derivative assets	0	0
Private equity investments	0	0
Total assets	464	369
Liabilities [Abstract]
Derivative liabilities	0	0
Securities sold short	0	0
Total liabilities	0	0
Level 2
Assets
AFS securities	23,879	24,109
LHFS at fair value	1,022	1,099
MSRs	0	0
Trading and equity securities	672	270
Derivative assets	183	437
Private equity investments	0	0
Total assets	25,756	25,915
Liabilities [Abstract]
Derivative liabilities	435	711
Securities sold short	145	120
Total liabilities	580	831
Level 3
Assets
AFS securities	407	432
LHFS at fair value	0	0
MSRs	1,179	1,056
Trading and equity securities	0	0
Derivative assets	3	6
Private equity investments	427	404
Total assets	2,016	1,898
Liabilities [Abstract]
Derivative liabilities	4	3
Securities sold short	0	0
Total liabilities	4	3
U.S. Treasury
Assets
AFS securities	2,378	2,291
U.S. Treasury \| Level 1
Assets
AFS securities	0	0
U.S. Treasury \| Level 2
Assets
AFS securities	2,378	2,291
U.S. Treasury \| Level 3
Assets
AFS securities	0	0
GSE
Assets
AFS securities	198	179
GSE \| Level 1
Assets
AFS securities	0	0
GSE \| Level 2
Assets
AFS securities	198	179
GSE \| Level 3
Assets
AFS securities	0	0
Agency MBS
Assets
AFS securities	20,372	20,101
Agency MBS \| Level 1
Assets
AFS securities	0	0
Agency MBS \| Level 2
Assets
AFS securities	20,372	20,101
Agency MBS \| Level 3
Assets
AFS securities	0	0
States and political subdivisions
Assets
AFS securities	771	1,392
States and political subdivisions \| Level 1
Assets
AFS securities	0	0
States and political subdivisions \| Level 2
Assets
AFS securities	771	1,392
States and political subdivisions \| Level 3
Assets
AFS securities	0	0
Non-agency MBS
Assets
AFS securities	529	576
Non-agency MBS \| Level 1
Assets
AFS securities	0	0
Non-agency MBS \| Level 2
Assets
AFS securities	122	144
Non-agency MBS \| Level 3
Assets
AFS securities	407	432
Other
Assets
AFS securities	38	8
Other \| Level 1
Assets
AFS securities	0	6
Other \| Level 2
Assets
AFS securities	38	2
Other \| Level 3
Assets
AFS securities	$ 0	$ 0

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