Loans and Allowance for Loan Losses - Loans in Commercial Portfolio Segment Monitored for Credit Quality Revolving and Non Revolving Loans (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Credit quality of consumer loans
Financing receivable	$ 78,567	$ 82,166
Commercial
Credit quality of consumer loans
2020	$ 3,912	$ 8,899
2020 Percentage	8.00%	17.00%
2019	$ 6,947	$ 7,275
2019 Percentage	14.00%	15.00%
2018	$ 6,788	$ 5,700
2018 Percentage	14.00%	11.00%
2017	$ 5,144	$ 2,974
2017 Percentage	10.00%	6.00%
2016	$ 2,739	$ 2,434
2016 Percentage	5.00%	5.00%
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	$ 7,152	$ 5,875
Prior Percentage	14.00%	12.00%
Financing Receivable, Revolving	$ 17,452	$ 16,992
Revolving Percentage	35.00%	34.00%
Financing receivable	$ 50,134	$ 50,149
Total	100.00%	100.00%
Commercial | Commercial and industrial | Pass
Credit quality of consumer loans
2020	$ 2,720	$ 6,444
2019	4,594	2,207
2018	1,976	1,592
2017	1,328	990
2016	983	697
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,814	1,477
Financing Receivable, Revolving	16,553	15,693
Commercial | Commercial and industrial | Special Mention
Credit quality of consumer loans
2020	3	30
2019	28	182
2018	215	128
2017	38	64
2016	53	30
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	80	96
Financing Receivable, Revolving	532	724
Commercial | Commercial and industrial | Classified
Credit quality of consumer loans
2020	19	79
2019	136	76
2018	53	155
2017	210	41
2016	12	1
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	43	35
Financing Receivable, Revolving	242	471
Commercial | Commercial mortgage | Pass
Credit quality of consumer loans
2020	817	1,636
2019	1,575	3,730
2018	3,612	2,778
2017	2,766	1,708
2016	1,594	1,527
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	4,243	3,180
Financing Receivable, Revolving	92	65
Commercial | Commercial mortgage | Special Mention
Credit quality of consumer loans
2020	1	16
2019	18	109
2018	68	245
2017	133	44
2016	42	54
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	42	194
Financing Receivable, Revolving	0	15
Commercial | Commercial mortgage | Classified
Credit quality of consumer loans
2020	46	1
2019	1	102
2018	95	351
2017	341	8
2016	5	69
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	446	412
Financing Receivable, Revolving	0	0
Commercial | Construction | Pass
Credit quality of consumer loans
2020	243	305
2019	303	717
2018	628	321
2017	266	74
2016	7	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	11	2
Financing Receivable, Revolving	33	24
Commercial | Construction | Special Mention
Credit quality of consumer loans
2020	0	1
2019	0	12
2018	5	108
2017	61	36
2016	37	8
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Commercial | Construction | Classified
Credit quality of consumer loans
2020	0	0
2019	0	0
2018	0	21
2017	0	9
2016	6	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	7	17
Financing Receivable, Revolving	0	0
Commercial | Lease financing | Pass
Credit quality of consumer loans
2020	63	387
2019	292	140
2018	136	1
2017	1	0
2016	0	48
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	466	462
Financing Receivable, Revolving	0	0
Commercial | Lease financing | Special Mention
Credit quality of consumer loans
2020	0	0
2019	0	0
2018	0	0
2017	0	0
2016	0	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Commercial | Lease financing | Classified
Credit quality of consumer loans
2020	0	0
2019	0	0
2018	0	0
2017	0	0
2016	0	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	0	0
Financing Receivable, Revolving		$ 0