Supplemental information to the Consolidated Statement of Cash Flows - Footnote (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201602Member	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201802Member
Premises and equipment/operating lease obligations	$ 126	$ 1,440
New or Modified Leases
Lessee, Lease, Description [Line Items]
Premises and equipment/operating lease obligations		196
Cumulative Effect, Period Of Adoption, Adjustment
Lessee, Lease, Description [Line Items]
Premises and equipment/operating lease obligations		$ 1,244