Loans and Related Allowance for Credit Losses (Rollforward of Allowance for Loan and Lease Losses and Associated Loan Data) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 2,742	$ 2,629
Charge-offs	(618)	(442)
Recoveries	170	164
Net (charge-offs)	(448)	(278)
Provision for credit losses	3,172	369
Net (increase) / decrease in allowance for unfunded loan commitments and letters of credit		(6)
Other		7
Loans collectively evaluated for impairment - associated allowance		2,230
Ending balance	5,928	2,721
Loans collectively evaluated for impairment		232,525
Fair value option loans		755
Purchased impaired loans		1,871
Total loans		237,215
TDRs [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Loans individually evaluated for impairment - associated allowance		156
Loans individually evaluated for impairment		1,777
Other Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Loans individually evaluated for impairment - associated allowance		53
Loans individually evaluated for impairment		287
Purchased Impaired Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Impaired loans - associated allowance		282
Total commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,812	1,663
Charge-offs	(205)	(84)
Recoveries	39	40
Net (charge-offs)	(166)	(44)
Provision for credit losses	2,039	187
Net (increase) / decrease in allowance for unfunded loan commitments and letters of credit		(7)
Other
Loans collectively evaluated for impairment - associated allowance		1,713
Ending balance	3,380	1,799
Loans collectively evaluated for impairment		160,920
Purchased impaired loans
Total loans		161,603
Total commercial | TDRs [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Loans individually evaluated for impairment - associated allowance		33
Loans individually evaluated for impairment		396
Total commercial | Other Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Loans individually evaluated for impairment - associated allowance		53
Loans individually evaluated for impairment		287
Total commercial | Purchased Impaired Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Impaired loans - associated allowance
Total consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	930	966
Charge-offs	(413)	(358)
Recoveries	131	124
Net (charge-offs)	(282)	(234)
Provision for credit losses	1,133	182
Net (increase) / decrease in allowance for unfunded loan commitments and letters of credit		1
Other		7
Loans collectively evaluated for impairment - associated allowance		517
Ending balance	$ 2,548	922
Loans collectively evaluated for impairment		71,605
Fair value option loans		755
Purchased impaired loans		1,871
Total loans		75,612
Total consumer | TDRs [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Loans individually evaluated for impairment - associated allowance		123
Loans individually evaluated for impairment		1,381
Total consumer | Purchased Impaired Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Impaired loans - associated allowance		$ 282