Asset Quality - Changes in Allowance for Loan and Lease Losses by Loan Category (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 900	$ 883
Provision	339	64
Charge-offs	(101)	(87)
Recoveries	17	23
Ending balance	1,359	883
Total ALLL, including discontinued operations	1,402	896	$ 1,145	$ 910	$ 897
Total provision, including discontinued operations	342	66
Total charge-offs, including discontinued operations	103	91
Total recoveries, including discontinued operations	18	24
Provision for losses on lending-related commitments	20	(2)
Commercial Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	751	743
Provision	250	35
Charge-offs	(65)	(53)
Recoveries	6	12
Ending balance	818	737
Consumer Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	149	140
Provision	89	29
Charge-offs	(36)	(34)
Recoveries	11	11
Ending balance	541	146
Commercial and Industrial [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	551	532
Provision	187	24
Charge-offs	(60)	(36)
Recoveries	5	10
Ending balance	542	530
Commercial Mortgage [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		142
Provision	50	6
Charge-offs	(3)	(5)
Recoveries	1	1
Ending balance	207	144
Construction Loans [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	22	33
Provision	10	(1)
Charge-offs	0	(4)
Recoveries	0	0
Ending balance	25	28
Commercial Real Estate [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		175
Provision	60	5
Charge-offs	(3)	(9)
Recoveries	1	1
Ending balance	232	172
Commercial Lease Financing [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	35	36
Provision	3	6
Charge-offs	(2)	(8)
Recoveries	0	1
Ending balance	44	35
Real Estate - Residential Mortgage [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		7
Provision	5	1
Charge-offs	0	(1)
Recoveries	0	1
Ending balance	89	8
Home Equity Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	31	35
Provision	8	3
Charge-offs	(4)	(4)
Recoveries	2	2
Ending balance	184	36
Consumer Direct Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	34	30
Provision	29	12
Charge-offs	(12)	(10)
Recoveries	2	1
Ending balance	116	33
Credit Cards [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		48
Provision	31	8
Charge-offs	(11)	(11)
Recoveries	2	2
Ending balance	104	47
Consumer Indirect Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	30	20
Provision	16	5
Charge-offs	(9)	(8)
Recoveries	5	5
Ending balance	48	22
Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	10	14
Provision	3	2
Charge-offs	(2)	(4)
Recoveries	1	1
Ending balance	$ 43	$ 13