Loans and Allowance for Loan Losses - Nonaccural Loans (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Nonaccrual loans
Financing Receivable, Nonaccrual	$ 328	$ 421
Troubled debt restructured loans that continue to accrue interest	392	299
Troubled debt restructured nonaccrual loans (included in total nonaccrual loans above)	171	136
Commercial | Commercial and industrial
Nonaccrual loans
Financing Receivable, Nonaccrual	175	269
Commercial | Commercial mortgage
Nonaccrual loans
Financing Receivable, Nonaccrual	15	12
Consumer | residential mortgage and home equity [Member]
Nonaccrual loans
Financing Receivable, Nonaccrual	137	139
Consumer | Other Consumer Loans [Member]
Nonaccrual loans
Financing Receivable, Nonaccrual	1	1
Consumer Portfolio Segment [Member]
Nonaccrual loans
Financing Receivable, Nonaccrual	138	140
Commercial Portfolio Segment [Member]
Nonaccrual loans
Financing Receivable, Nonaccrual	$ 190	$ 281